PBIMABY DIVISIONS AND CLASSES. 221 



have, on the contrary, an aquatic and branchial respiration, 

 and which have always from five to seven pairs of limbs 

 adapted for locomotion.* 



The division of vermes or worms ought to comprise also 

 several very distinct types. There is first the annelides 

 (Pig. 175), whose ganglionary system is quite distinct through- 

 out its whole length, with red blood generally circulating in 

 a very complex vascular system, in which the respiration almost 

 always takes place in a well- developed branchial apparatus, 

 and in which the movements are performed in general by 

 means of moveable bristles (Fig. 176) ; with these also we 

 arrange the rotifera, microscopic animals, which seem to 

 have no special organs for the circulation, and which have no 

 branchiae, but which have in general vibratile organs very 

 singular in their arrangement (Fig. 177). Finally, it is 

 also to this primary division that we must refer the tur- 

 bellaria, whose body is without limbs, and whose nervous 

 system is composed essentially of two lateral cords springing 

 from two cephalic ganglions. The intestinal worms, or 

 helminthise, belong also to this division ; their structure is 

 very simple ; they present only vestiges of a nervous sys- 

 tem, and yet are intimately allied to the annelides, which 

 often seem to be in some measure the degraded representatives 

 of the same zoological type.f 



To place the classification of annul ated animals in harmony 

 with the differences which we have pointed out in the nature 

 of these beings, they must be divided into eight distinct 

 classes, the names of which we have already pointed out in 

 the preceding considerations. 



381. The primary division of the molluscous animals 

 presents organic modifications necessitating a similar subdivi- 

 sion. In the molluscs, properly so called, there is a nervous 

 system, composed of two or more pairs of nervous ganglions, 

 reunited by medullary cords (Fig. 179) ; and reproduction is 

 accomplished only by means of eggs. In others, which I 

 shall call mollusco'ides, the nervous system, reduced to a rudi- 

 mentary state, seems to consist of only a single ganglion, and 

 in most cases the multiplication of individuals takes place 

 by the development of granulations (bourgeons) as well as 



* It has been known for some years that the cirrhipedes, which had been 

 formed into a particular class, ought to be restored to the class Crustacea. 



f Naturalists are not agreed in respect of the classification of the entozoa, 

 or intestinal worms. Cuyier arranged them amongst the radiata or zoophytes ; 

 but they more resemble the annelides in the conformation of their bodies. 



