EMBRYOLOGTCAL SYSTEMS. 



3G9 



testing the value of the different kinds of groups gene- 

 rally adopted in our classifications, and this was, from 

 the beginning, my principal object in this inquiry. 1 The 



1 In this edition of the Essay on 

 Classification, which is intended as 

 an Introduction to the study of Na- 

 tural History in general, Van der 

 Hoeven's Text-book deserves more 

 than a passing notice, especially since 

 its translation by Professor Clark is 

 likely to be in the hands of every 

 English student of Natural History. 



The manner in which the charac- 

 teristics of the minor groups are pre- 

 sented in this work is so admirable, 

 the reference to the proper authori- 

 ties so full, the evidence of a personal 

 acquaintance with the objects de- 

 scribed so general, and the freedom 

 from mere compilation so praise- 

 worthy, that it is not only to be con- 

 sidered as a text-book for beginners, 

 but truly as a compendium of the 

 present state of Zoology, that may 

 be useful even to the professional 

 naturalist. 



Although taking the views of Cuvier 

 respecting the primary divisions of 

 the Animal Kingdom as a guide, the 

 author does not seem to hold them 

 of such importance, or sufficiently 

 defined, to deserve a special consider- 

 ation. He has thus deprived himself, 

 in a great measure, of the opportu- 

 nity of presenting in a connected 

 manner, those broader generaliza- 

 tions respecting the affinities and 

 homologies of the different classes of 

 animals, which, however, constitute 

 the most important progress of mo- 

 dern Zoology, and have secured for 

 our science so important a place 

 among the philosophical studies of 

 our age. It seems to me also that, 

 though not entirely neglected, the 

 history of the fossil remains is not 

 sufficiently prominent, and the man- 

 ner in which they are frequently pre- 

 sented, without connexion with the 

 living types, is particularly unfa- 

 vourable to a true appreciation of 

 their natural relation to their living 



representatives. The time has truly 

 come when the whole Animal King- 

 dom should be represented in its 

 development through all geological 

 periods as fully as the mode of growth 

 of the living is, in our days, connected 

 with their general history. 



Respecting the classes, I believe, 

 for reasons already stated (see p. 289), 

 that the Infusoria ought to be divided 

 off according to their natural affinity, 

 partly among the Algfe, partly among 

 the Worms, and partly among the 

 Bryozoa. The relation of the Rhizo- 

 pods to the lower Algte, and especi- 

 ally to the Corallines, seems to me 

 daily more probable, and I consider 

 the evidence thus adduced of the 

 vegetable character of the Anentera 

 as amounting almost to a demonstra- 

 tion. 



In the class of Acalephs, the Cteno- 

 phorte occupy a position inferior to 

 the Discophorae. It seems to me 

 hardly questionable that they should 

 occupy the highest position in that 

 class. The Sipunculidsa, which I am 

 inclined to refer to the class of worms, 

 are included among the Echinoderms. 

 The ambulacral system, with or with- 

 out external suckers, constitutes the 

 essential character of the Echino- 

 derms. Sipunculus has none. The 

 distinction of the intestinal worms 

 and the Annulata as two distinct 

 classes, separated by the Rotatoria, 

 seems to me unnatural. The Turbel- 

 laria and Suctoria unite the Annu- 

 lata with the Trematodes and other 

 worms as one class, and the most re- 

 cent investigations show unquestion- 

 ably that the Rotatoria are Crusta- 

 cea. It seems to me also unnatural 

 to separate the insects and spiders 

 as two classes. The Tardigrada and 

 Acarina form the transition to the 

 PoduraandEpizoa. The class of Crus- 

 tacea, though well defined, if we add 

 the Rotatoria to it, should be placed 



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