CLASSIFICATION OF ANIMAtS. 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 nervous system could be most unequivocally traced in a 

 filamentary form, likewise presented an alimentary canal as a distinct 

 tube, with a mouth and anus, suspended in a distinct abdominal 

 cavity : the well-defined nerves governed a corresponding develop- 

 ment of the muscular system. Generation was by impregnated ova, 

 never by spontaneous fission or gemmation. 



The Echinoderma, Rotifer a, Ccelelmi7ithay and Ciliobrachiatay are 

 the classes of Cuvier's zoophytes, which were 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 with it testimony of its 

 presence in animalcules where it had not before been detected. 

 Nevertheless, in those classes in which the 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 Polygasfria, the generative 

 organs in the TcenicB, 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 I 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 embryo forms of the higher classes ; and as the several changes 

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

 so also each class of the Acrita more closely approximates some class 

 of the Nematoneura than is observed in the classes of the higher 

 groups, and the characters 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 col- 

 lective names, as in this 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. 



