PRIMABY DIVISIONS AND CLASSES. 203 



vertical line, so as to affect a radiated disposition more or 

 less complete. With regard to a nervous system, no trace is 

 generally to be observed, and where it exists, it is reduced to 

 a rudimentary state; the organs of the senses are also 

 almost completely wanting ; finally, all the parts of the eco- 

 nomy become of an extreme simplicity. For a long time 

 they were mistaken for vegetables, and hence their name of 

 zoophyte or animal plants, and they have been called radiated 

 animals, by reason of the obvious radiated disposition of their 

 organs. The polyps, of which we have already spoken 



c v ap p r 



e d pi 



Fig. 144. Anatomy of the Colimacon, or Snail.* 



( 347), the actiniae or sea anemones (Fig. 145), and 

 the asteria or sea star (Fig. 136), are specimens of this 

 division.f 



378. Subdivisions of the Primary Division into 



* pi, the foot ; t, tentacle, half contracted ; d, a sort of diaphragm sepa- 

 rating the respiratory cavity from the other viscera; e, portion of the 

 stomach; f, the liver; o, the ovary; i, intestines; r, rectum; a, anus; 

 c, the heart, the pericardium has been opened; ap, pulmonary artery, 

 ramifyingon the walls of the pulmonary cavity, p; ar, aorta; v, gland, secreting 

 the viscosity; c e, its excretory canal opening near the anus. 



t Some zoologists admit a fifth primary division of the animal kingdom, 

 comprising sponges, and characterized by the absence of all regular form. 

 But it seems to us that this classification ought not to be adopted, for these 

 strange animals (amorphozoaria) present when young the same characters as 

 polyps, only their organic development is arrested at a transitory state, and 

 they become deformed as they grow older. Thus by keeping in view their 

 mode of development, they may be referred to the class zoophytes. 



