410 PHYSIOLOGY. 



i. Group - GASTROZOA. The following classes belong here : 



1. Infusoria polygastrica. Ehrenb. 2. Polypina sive 

 Corallina. 3. Medusina. 4. Echinodermata. 

 5. Mollusca. Cuv. 

 n. Group ARTHROZOA. Here belong the classes : 



6. Endozoa. Annulata. 7- Rotatoria. Crustacea. 



8. Myriapoda. Arachnodea. 9. Insecta. 

 ill. Group OSTEOZOA : 



10. Pisces. 11. Amphibia. 12. Aves. 13. Mammalia. 



246. 



The forms of the thus discovered three chief groups of the animal 

 kino-dom are adapted precisely to their internal organisation. The 

 first group possess a figure conformable to its organisation, namely, 

 that of a bag or sack, that it may receive in this sack its various 

 organs. In the highest animals, also, the same organs which in 

 animals of the first series are especially developed, also lie in large 

 cavities and bags, that are formed almost exclusively of soft parts. The 

 second group, which is constructed upon the predominant development 

 of the organs of motion, exhibits an elongate form, generally divided into 

 segments and limbs. Herein also they correspond in form with the 

 same organs of the higher animals, which characterise the second 

 series in the development of the animal kingdom, namely, the members, 

 which, as well as them, are elongate, and consist of joints and conse- 

 cutive divisions. The third group, consisting of the conjunct contents 

 of both the others, has a form partaking of that of both ; their bodies, 

 consequently, appear as central bags and cavities, whence the peri- 

 phrastic subdivided members proceed. They thus, therefore, repeat 

 the forms of all the other animals ; indeed, their form is, as it were, a 

 compilation of all other animal forms. 



247. 



Insects, consequently, by reason of the predominant development of 

 their organs of motion, belong to the elongate animals, divided into 

 segments and divisions. By means only of such a structure is free 

 motion possible. One limb pushes itself forward, affixes itself, and 

 draws the other after it; the alternating, affixing, and quitting is 

 repeated then by every successive limb, and thus the general motion of 



