Dajaus diemensis See Mullets

Damselfishes Fishes of the Family Pomacentri-dae, formerly a part of the *chromids, particularly abundant on coral reefs, to which they add their own tufts of colours, as flowers do to spring meadows. Some damselfish species actively 'farm' filamentous *algae as a food source, defending their meadows vigorously against competitors and even large predatory fishes (Zeller 1988).

CD collected two species of this family during the voyage of the Beagle. The first was the Cape Verde gregory Stegastes imbricatus Jenyns, 1840, whose original description is based on a specimen of 3 inches from Quail Island, in the bay of Puerto Praya, *Cape Verde Islands (Fish,pp. 63-5, 165; Fish in Spirits,after no. 157; Fig. 7). The Cape Verde gregory, which reaches 10 cm, lives on rocky bottoms down to a depth of 25 m, and ranges, along the West African coast, from the Canaries and Senegal in the North to Angola in the South.

The second specimen, which was Above leaden colour, beneath paler, grows considerably larger, was sampled near *Valparaiso, Chile. It belongs to Chromis crusma (Valenciennes, 1833), and was described as Heliases crusma (Fish, pp. 54-6; Fish in Spirits, no. 1011).

CD never returned to the damselfishes. Nevertheless, this group includes a Darwin *eponym, Pomacentrus darwiniensis, now Dischis-todus darwiniensis (Whitley, 1928).

DAR Abbreviation for 'Darwin Archive,' used, for example, by the editors of CD's * Correspondence. The Darwin Archive, kept partly at the Cambridge University Library and partly at the Darwin family's 'Down House', England, has

Fig. 7. Cape Verde gregory Stegastes imbricatus, of the Family Pomacentridae, or damselfishes. Based on a specimen taken by CD near Quail Island, Puerto Praya, Cape Verde Islands (Fish, Plate IX).

been extensively mined by Darwin scholars, although there are still parts that have not been transcribed, including some that would have been useful for this book. This applies particularly to his Experimental Book (DAR 157a), and to various smaller items scattered throughout this volume, which are cited here from secondary sources.

darwin(s) Unit of relative change in the structure of organisms, proposed by Haldane (1949a), with one 'darwin' corresponding to the difference between the natural logarithms of two measurements (x1, x2), reflecting change in an attribute, divided by the corresponding time difference in million years ((ln x2 - ln x1)/(t2 -t1)). This unit has several deficiencies, but still can be used to illustrate some issues, notably concerning *punctuated equilibrium.

Darwin, Charles Robert The person here referred to as 'CD', born on February 12,1809,who died on April 19,1882, and whose published work (listed in Freeman 1977), especially Darwin (1859), changed the way humans see themselves.

There are numerous biographies of CD. Among the recent ones, the best are probably those by Desmond and Moore (1992), and Browne (1995, 2002), and there is no point in this book attempting to substitute for these. For the limited biographic information in this book, see Autobiography, Beagle, and Jenyns.

Darwin's Bass Title of a book by Quinnett (1996), and largely delivering on its ambitious subtitle: The Evolutionary Psychology of FishingMan.

Here Darwin's bass - the Largemouth bass Micropterus salmoides (Lacepede, 1802) - is the great survivor, which, having learnt to avoid the lures of the clumsy angler, gives such challenge to the sophisticated one. As this war of wits and technology (carbon fibre rods, plastic lures) escalates over bass generations, continued angling pleasure is guaranteed to successive generations ofanglers - given that they do not overfish, and that we humans do not trash our planet.

The depth of thought - and of feelings -and the soundness ofthe scientific observations playfully presented in Darwin's Bass make it the contemporary counterpart of *Walton's Com-pleat Angler, which CD used to consult. Thus, Darwin's Bass somehow closes a cycle, at least within this book.

Darwin's Finches A group of small birds of the genus Geospiza, whose different morphology, specific to each of the *Galapagos Islands, is often believed to have given CD, while he was on these islands, the key to what later became his theory of *natural selection. In reality, CD failed to notice these inter-island differences, and they were brought to his attention much later by John Gould, when the latter was working on the material for *Birds (Gould etal. 1841; Lack 1953).

Still, Darwin's Finches inspired this book.

Darwin's Fishes CD's interest in coral reefs, *barnacles, *worms, and orchids is well documented and, indeed, his work led to monographs now essential to those working on these groups.

Not so for fishes: although he was interested in this group, as attested by numerous observations scattered throughout his published work, and his *notebooks and Correspondence, CD never authored any book or paper devoted solely, or even mainly to fishes. Thus, ichthyologists and Darwin scholars interested in CD's treatment of this most speciose group among the vertebrates, until now had to content themselves with *Fish, a book edited, rather than authored, by CD.

The present volume addresses this by covering all the fishes (over 250 species) with which CD can be associated, i.e., 'Darwin's Fishes.' (The pun is intended, and it works also in French: les poissons de Darwin - les pinsons de Darwin). Graphically, this is:

Deep-sea spiny eels or abbreviated, and as a *shoal:

<°cd >{ <°cd>{ <°cd >{ <°cd >{ <°cd >{ <°cd >{

The single version somehow resembles a (European) mackerel (Scomber scombrus), while the fish in the shoal resemble Indo-Pacific mackerel (genus Rastrelliger), both taxa not mentioned elsewhere in this book.

The first group of Darwin's Fishes (n = 137) consist of the species collected by CD during the voyage of the *Beagle; the overwhelming majority of those were described by *Jenyns in *Fish.

The second group of'Darwin's Fishes' (n = 91) are those mainly European species whose biology CD commented upon, either in his formal publications, or in his notebooks, correspondence or *marginalia. Jointly, these two groups make up 5.7% of the 4152 fish species which, according to *FishBase, had been formally described before 1850 (the year taken here to represent the midpoint of CD's ichthy-ological work).

The third group are the *eponyms, i.e. the fish species named after CD (n = 17), e.g. the *wrasse Pimelometopon darwini.

There is very little overlap between these three groups: the biological information on the species he collected during the voyage of the Beagle was too limited to illustrate the broader principles CD was interested in. Thus, he relied for the bulk ofhis post-Beagle writings on well-studied European species (e.g. *Pike), though with some interesting exceptions (e.g. *Galaxi-idae; *Goldfish). Fortunately, CD never commented on the fishes named after him, or after Port Darwin, thus saving us from having to coin a term for the semantico-epistemological conundrum this would have created.

An additional 72 fish species are introduced to illustrate various issues, bringing the number of fishes mentioned in this book to a total of320 species, i.e. roughly 1%of the extant fish species, including those still to be described (see FishBase; Ichthyology).

Darwin's roughy Common name of Gephyroberix darwinii (Johnson, 1866), also known as Finescale roughy (Gomon et al. 1994, pp. 4001), a member of the Family Trachichthyidae (slimeheads, roughies and sawbellies), previously Trachichthys darwinii, and still an *eponym. The famously long-lived (up to 149 years; Fenton et al. 1991) Orange roughy Hoplostethus atlanticus Collett, 1889 is a close relative.

Deal fish Common name of Trachipterus arcticus (Brunnich, 1788), also known as Ribbon fish, and a species that may be seen as providing a model for the evolutionary transition toward the peculiar adaptations of flatfishes. Thus, CD mentions that certain species, whilst young, habitually fall over and rest on the left side, and other species on the right side. Malm adds, in confirmation ofthe above view, that the adult Trachypterus arcticus, which is not a member of the Pleuronectidae, rests on its leftside at the bottom, and swims diagonally through the water; and in this fish, the two sides ofthe head are said to be somewhat dissimilar. Our great authority on fishes, Dr.*Giinther, concludes his abstract of Malm's paper, by remarking that 'the author gives a very simple explanation of the *abnormal condition of the Pleuronec-toids.' (Origin, VI,p. 187;Malm 1868,abstracted in Gunther 1868b).

The deal, here, is that the transition from bilaterally symmetrical fishes to fishes that swim on the side is easy to conceive, notwithstanding the issues that led to what may be called the first *Flatfish controversy.

Deep-sea spiny eels A family of eel-like fishes with a global distribution, the Notacanthidae, whose species feed mainly on *zoobenthos at depths ranging from 125 to 3500 m.

CD, citing Richardson (1846, pp. 189,191), mentions the genus Notacanthus only once, in conjunction with the phenomenon now known as *submergence: Notacanthus & *Macrourus [are] two very remarkable Greenland genera,

Development which inhabit deep water, [and] have recently been discovered on the coast of New Zealand & S. Australia. (BigSpeciesBook, p. 555).

Here, CD was probably referring to the Spiny eel Notacanthus chemnitzii Bloch, 1788, which ranges in the North Atlantic from Northwestern Greenland to South Africa, and in the Pacific from Chile to New Zealand and Australia. This species, incidentally, is reported to feed heavily on CD's *Zoophites, i.e. sea anemones (Sulak 1990), certainly an interesting adaptation.

Descent Short title of The Descent of Man, and Selection in Relation to Sex (Darwin 1877b), probably CD's most daring work, as it deals with a species - Homo sapiens - he avoided in Origin.

Descent provided six figures and text material for numerous entries in this book, on, for example, *seasquirts, Professor Mobius' *Pike, and *sexual selection, here illustrated by one of its results, *sexual dimorphism. The many cases illustrating this, and pertaining to fishes (in Chapter XII, pp. 330-47) are presented here on a per-species basis, much of it based on information supplied by *Giinther. Indeed, CD thanked him for having helped transform this chapter from much the worst into one of the best (July 15,1870, Calendar, no. 7276; see the Calendar for CD's other, so far unpublished, letters on this).

Development Also known as *ontogeny, the development of an individual from a fertilized egg to the adult form involves a series of stages which many biologists, foremost *Haeckel, have likened to a 'recapitulation' of their ancestors' different morphologies. CD deals with this and related issues of *embryology repeatedly, with fish being frequently invoked, e.g. In early stage, the wing of *bat, hoof, hand, paddle are not to be distinguished. At a still earlier <stage> there is no difference between fish, bird, etc. and mammal. It is not that they cannot be distinguished, but the arteries <illegible>. It is not true that one passes through the form of a lower group, though no doubt fish more nearly related to foetal state.55

This similarity of the earlieststage is remarkably shown in the course of the arteries which become greatly altered, as foetus advances in life and assumes the widely different course and number which characterize full-grown fish and mammals. How wonderful that in egg, in water or air, or in womb of mother, artery should run in same course. (Foundations, p. 42; n. 55, originally written across the page: They pass through the same phases, but some, generally called the higher groups, are further metamorphosed. [line break] .'Degradation and complication? No tendency to perfection. [line break]? Justly argued against *Lamarck.?). And: There is no object gained in varying form, etc. of foetus (beyond certain adaptations to mother's womb) and therefore selection will not further act on it, than in giving to its changing tissues a tendency to certain parts afterwards to assume certain forms.

Thus there is no power to change the course of the arteries, as long as they nourish the foetus; it is the selection of slight changes which supervene at any time during <illegible> of life.

The less differences of foetus - this has obvious meaning on this view: otherwise how strange that a [monkey] horse, a man, a bat should at one time of life have arteries, running in a manner, which is only intelligibly useful in fish! The natural system being on theory genealogical, we can at once see, why foetus, retaining traces of the ancestral form, is of the highest value in classification. (Foundations, pp. 43-5). Further, arguing against the likelihood ofseparate creation for three species of rhinoceros in Java, Sumatra and Peninsular Malaysia, respectively, CD rhetorically asks what we are to make of the fact That in possessing [...] useless abortive teeth, and in other characters, these three rhinoceroses in their embryonic state should much more closely

Difficulties resemble other mammalia than they do when mature. And lastly, that in a still earlier period oflife, their arteries should run and branch as in a fish, to carry the blood to gills which do not exist. (Foundations, p. 250).

Devonian A series of Paleozoic rocks, including the Old Red Sandstone (Origin VI, p. 423). Named after Devonshire, in England, and pertaining to times between 418 and 362 million years ago, right after the *Silurian, and before the Carboniferous.

The Devonian is often referred to as the 'Age of Fishes' because of the flourishing, during that period, of many now extinct fish groups (see Moy-Thomas 1971).

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