Lefevre — The Advance of Zoology in the Nineteenth Century. 85 



time down to the beginning of the last decade. Science does 

 not develop logically, but follows the paths of least resistance ; 

 and with the almost endless wealth of material at hand, made 

 especially easy of access by the establishment of many marine 

 laboratories along the coasts of Europe and America, and 

 augmented by the rich collections brought back by scientific 

 expeditions, it is not surprising that so fascinating a study 

 should have absorbed zoologists for a long time. During the 

 past ten years other problems have occupied the attention of 

 investigators to a greater degree, and phylogenetic researches 

 have been going out of fashion. 



It would be an impossible task to speak here of the count- 

 less discoveries made in the field of comparative anatomy and 

 embryology under the inspiration of the doctrine of descent, 

 for our modern knowledge in these branches, which has 

 largely been the outcome of researches carried on during this 

 period, has attained enormous proportions. Our present 

 system of classification, which attempts to express the proba- 

 bilities of genealogical relationships, embodies the results of 

 our anatomical and embryological knowledge of to-day. Every 

 group of animals has been most carefully studied, its anatomy 

 and development accurately described and pictured, and 

 although gaps exist here and there, the amount of information 

 which we now possess was undreamed of even in Darwin's 

 time. Old groups have been broken up and several classes 

 made of them, as for example, the Mollusca, which has 

 been forced to surrender the Brachiopoda, the Bryozoa 

 and the Tunicata, as more careful anatomical and embryolog- 

 ical study has brought to light their special affinities. The 

 group of Vermes which so long remained the dumping ground 

 for all forms whose relationships were obscure has in the 

 latest proposed classification been discarded altogether and it 

 is now represented by a number of separate branches. We 

 now recognize twelve phyla, or main subdivisions of the 

 animal kingdom, including fifty-one classes and several 

 appendices, or groups whose affinities are doubtful. It is 

 probable, however, that any classification will receive only a 

 temporary acceptance, and will for a long time to come be 

 subject to much remodeling and revision, as discoveries are 

 made which necessitate change. 



