248 



NATURE 



[July 59, 1875 



are rather theoretical than practical. Prof. Cams suffers 

 in this book as in his " History " of Zoology, from the un- 

 philosophic conception of the scope and tendencies of 

 that division of Biology, which its early history has forced 

 upon modern science. In England our newest and most 

 conservative University continues to draw a broad dis- 

 tinction between what is called Comparative Anatomy 

 and what is called Zoology. By some accident Zoology 

 is the term which has become connected with the special 

 work of arranging specimens and naming species which 

 is carried on in great museums, and which has gone on in 

 museums since the days when " objects of natural his- 

 tory," and other curiosities, first attracted serious attention 

 in the sixteenth century. Accordingly Zoology, in this 

 limited sense, has taken the direction indicated by the 

 requirements of the curators of museums, and is supposed 

 to consist in the study of animals not as they are in toto, 

 but as they are for the purposes of the species-maker and 

 collector. In this limited Zoology, external characters or 

 the characters of easily preserved parts which on account 

 of their conspicuousness or durability are valuable for the 

 ready discrimination of the various specific forms — have 

 acquired a first place in consideration to which their real 

 significance as evidence of affinity or separation does not 

 entitle them. From time to time the limited zoologists 

 have adopted or accepted from, the comparative anato- 

 mists hints or conclusions, and have worked them into 

 their schemes of classification. But it does seem to be 

 time in these days, when pretty nearly all persons are 

 agreed that the most natural classification of the Animal 

 Kingdom is that which is the nearest expression of the 

 Animal Pedigree, that systematic works on Zoology should 

 be emancipated from the hereditary tendencies of the old 

 treatises, and should present to us the classes and 

 orders of the Animal Kingdom defined not by the enu- 

 meration of easily recognised " marks," but by reference 

 to the deeper and more thorough-going characteristics 

 which indicate blood relationships. We have to note in 

 the " Handbuch " the not unfrequent citation of superficial 

 and insignificant characteristics in the brief diagnoses of 

 taxonomic groups, which seems in so excellent a work to 

 be due to a purposeless survival of the features of a mori- 

 bund zoology thatiWOuld know nothing of " insidcs," and 

 still less of the doctrine of filiation. For instance, the 

 very first thing which we are told of the Vertebrata in the 

 short diagnosis of the group, is that they are " animals 

 with laterally symmetrical, elongated, externally unseg- 

 mented bodies ; " of the Fishes, that they have the " skin 

 covered with scales or plates, seldom naked ; " of the 

 Mollusca, that they have a " laterally symmetrical, com- 

 pressed body devoid of segmentation, often enclosed in a 

 single (generally spirally-twisted) or double calcareous 

 shell." It would be unjust to suggest that Prof. Carus, 

 who long ago did so much to estabhsh zoological classi- 

 fication on an anatomical basis, is not fully alive to the 

 necessity, at the present day, of taking the wide bio- 

 logical view of animal morphology ; but certainly the 

 form in which parts of the book are cast, savours ot the 

 past epoch. It may be said that the object of the book 

 is to present the "facts" of Zoology in a logical order ; and 

 that this sufficiently explains the arrangements to which 

 objection might be taken as above, viz. the commencing 

 with the higher instead of the lower groups, the prominent 



position assigned to external and little-significant cha- 

 racters, the absence of any recognition of the leading 

 doctrine of modern Zoology, the doctrine of filiation. To 

 this there is nothing to say excepting that of the very 

 many logical methods of treatment possible in a hand- 

 book of Zoology, many are easy to follow out, and that 

 one, which aims at presenting a logical classification of 

 the kind spoken of by Mill, in which objects "are arranged 

 in such groups, and those groups in such an order as 

 shall best conduce to the ascertainment and remem- 

 brance of their laws," is a very difficult one to follow out. 

 This kind of classification involves nothing less than an 

 attempt (however inadequate) to trace the Animal Pedi- 

 gree ; for the laws to be ascertained and remembered are 

 the laws of Heredity and Adaptation. We may regret 

 then that so able a zoologist as Prof. Carus has remained 

 in the old grooves and not ventured on to the inevitable 

 track where Gegenbaur and Haeckel have preceded 

 him. 



It is in the same spirit that we draw attention to one 

 or two features in the logical — or as it is sometimes called 

 " objective " — classification adopted by Prof. Carus. He 

 recognises the MoUuscoidea as a main division of the 

 Animal Kingdom, and places in it besides the Brachio- 

 poda and the Bryozoa, the Tunicata. It certainly does 

 not seem likely that in the present year (which is that 

 which gives date to the volume containing the Mol- 

 luscoidea) he would, if attempting to indicate genea- 

 logical affinities in his classification, do what he does 

 whilst working on the old lines, namely, place the 

 Ascidians in association with forms so remote from them 

 as it now appears are the Brachiopods, and separate them 

 so entirely from their blood-relatives among Vertebrates. 



It is also interesting to note how the desire to frame 

 symmetrical groups which can be easily defined in a few 

 words, and on the other hand the desire to mark the gaps 

 and the relative development of the branches of the 

 genealogical .tree, operate so as to lead individuals in- 

 fluenced respectively by one or other of those desires to 

 propose very different changes in commonly accepted 

 classifications. Both methods may have their use to-day, 

 but we cannot shut our eyes to the fact that the motive in 

 all classifications for the future must be genealogy. The 

 changes proposed in J. Miiller's classification of Fishes, 

 respectively by Carus and by Haeckel, exhibit well the 

 divergence of the tendencies of the "formal" (we cannot 

 grant them the monopoly of the word " logical ") and of 

 the " genealogical " school. Dr. Giinther of the British 

 Museum is followed by Pi-of. Carus in his proposal to 

 reduce Johannes Miiller's six sub-classes of Fish, viz. 

 Dipnoi, Teleostei, Ganoidei, Selachii, Cyclostomi, Lepto- 

 cardii, to four, by the fusion of the Dipnoi, Ganoidei, and 

 Selachii. The discovery of the Australian Ceratodus, 

 which does not possess a special aortic branch distri- 

 buted to the incipient lungs, and is different from Lepido- 

 siren and Protopterus in the structure of its aortic bulb 

 and its limbs, has been made the occasion for this 

 logical or rather formal simplification. On the other 

 hand. Prof Haeckel wishing to show the large gap — the 

 long series of intermediate forms— which tmist have inter- 

 vened between the development of certain of the branches 

 of the pedigree recognised by J. Miiller as sub-classes of 

 Fish, and wishing to express the relative distance of 



