lU 



BIOLOGY. 



[Book ii. 



the emission and the retraction of the pseudopods. Liquid currents 

 charged with granules are visibly produced. 



In some infusoria we observe a rotatory movement, in a con- 

 stant direction, of the intracellular liquid, that is to say, a 

 phenomenon completely comparable with the intra-cellular gyra- 

 tion of the vegetal protoplasm (Paramsecia). 



Immediately after the protozoa come the animals a little more 

 complex, having a digestive cavity, but no other. These are the 

 coral polypi or anthozo'ids, the hydromedusce, the cienopkores. 

 In a certain number of animals of this group we see the first 

 rude beginning of the circulatory 

 apparatus, consisting of ramifications 

 more or less complex, emanating from 

 the digestive cavity and communicating 

 with it (medusae, and so on, — see Figure 

 6). The digestion and the circulation 

 being still confounded, we may charac- 

 terise the whole of the system as 

 gastro-vascular. The content of the 

 apparatus is not yet specialised : it is 

 chyme diluted with water. 



An organic progress is accomplished 

 in the noemathelmint/is. For the first 

 time the nourishing liquid elaborated 

 by the digestive apparatus is, befor^ 

 being assimilated, collected in a special 

 cavity distinct from the digestive system, 

 and surrounding it more or less com- 

 pletely. Figurate elements, a sort of 

 sanguineous globules, float in this liquid 

 in some nsematods. In the ncemertians 

 we already see appearing some vascular 

 canals. (Figure 15.) In the annelates there is a tolerably regular 

 network ; there are also longitudinal vessels connected with each 

 other, and of which one, very constant, is dorsal. This last is 



Fia. 15. 



Anterior extremity of the body 

 uf a naiinertian (Borla^M ca- 

 miUa) : a opening of the 

 trompe ; p, trompe ; c, vihratile 

 depressions ; %. cervical gang- 

 lion ; «', lateral nervous sys- 

 tem ; I, sanguineous lateral 

 tniuks, which bend forward in 

 order to unite : before this 

 union theysendround the brain 

 a branch which joins that op- 

 posite in order to form the 

 dorsal vessel {{. 



