CLASSIFICATION OF ANIMALS. 15 



The binary division, which I proposed in 1835*, has been adopted 

 in this country by my esteemed friend, the Professor of Comparative 

 Anatomy at King's College. I found that those Radiata of Cuvier 

 in which the nervovis system could be most unequivocally traced in a 

 filamentary form, likewise presented an alimentary canal, suspended 

 in a distinct abdominal cavity, and, with very few exceptions, pro- 

 vided with a distinct outlet : the well-defined nerves governed a cor- 

 responding development of the muscular system ; and generation was 

 always by impregnated ova. The Echinoderma, Rotifera, Ccelebnintha, 

 and Ciliobrachiata, were thus grouped together by positive characters, 

 under the title Nematoneura. 



I do not deny a filamentous condition of the nervous system 

 in the rest of the zoophytes; each day brings testimony of its 

 presence in animalcules where it had not before been detected. 

 Nevertheless, in those classes in which this condition of the nervous 

 system is most obscure, we find that the digestive cavity is generally 

 excavated in the common parenchyma of the body, is devoid of free 

 parietes, and has no anal outlet : particular organs are often inde- 

 finitely multiplied, as the stomach in the Polygastria, the generative 

 organs in the TcenicE^ the prehensile mouth in the Polypi : genera- 

 tion by gemmation and spontaneous fission is common in this lowest 

 division of the animal kingdom, to which 1 have applied the name 

 Acrita, which had been used in a more extended sense by Mr. Macleay. 

 Two classes, the Acalephce and Anthozoa (Ehrenberg), stand in an 

 intermediate position between the Acrita and Nematoneura ; and most 

 of the classes in the lowest division of the Radiata lead by more or 

 less gentle gradations into those of the higher one. 



Nor is this surprising : the radiated animals are closely analogous to 

 the embryonic states of the higher classes ; and as the earlier changes 

 of such embryos succeed each other more rapidly than the later ones, 

 so the Acrite classes more rapidly approximate or merge into the 

 Nematoneurous ones, than do the corresponding grades or classes of 

 the higher sub-kingdoms of animals ; and consequently the charac- 

 ters of the lowest or Acrite classes are the least definite and fixed. I 

 have, therefore, endeavoured to express the relations of the higher 

 and lower organised classes of the Radiata of Cuvier, by placing them 

 in parallel lines under their former collective names, as in the following 

 tabular diagram of the provinces and classes of the animal kingdom. 



* Syllabus of the Lectures on Comparative Anatomy, given at the Medical School 

 of St. Bartholomew's. 8vo. 



