.PHYSIOLOGY OF THE INVERTEBRATA. 119 



absorbed by the blood-vessels distributed 011 the walls of the 

 digestive system. Thi'ough the medium of blood-vessels the 

 products of digestion are carried to all parts of the body. 

 In tliis case there is a fusion of the functions of absorption 

 and circulation ; the products of digestion become incorpo- 

 rated with the blood ere they reach the tissues for which they 

 are destined. 



Therefore, in the Invcrtchrata the function of absorption 

 does not exist as an entirely separate function, as one finds in 

 the Vcrtcbrata. It is either fused with the function of 

 digestion or the function of circulation. 



The Protozoa. 



The (i /rtjnrinidc , being parasitic organisms, pass their 

 existence in the chyle or nutritive fluid of the higher animals. 

 They absorb by the whole surface of their bodies the nutritive 

 fluids of their hosts ; such Huids are already in such a state 

 as to form a nutritive material for these low organisms. 

 Probably the nutritive material does not undergo any fur- 

 ther change after passing into the body of a Gregarina. 

 '* Perhaps no other animals present such a complete want of 

 differentiation between the functions of digestion and ab- 

 sorption "" as do the Gre<jarinida. 



In the llkizoimda (e.g., Aimebd) food is taken in at any 

 part of the cell, but only at one region of the cell at one given 

 time — I.e., the whole surface of the cell can ingest food, but 

 only one portion of it ingests at a time. In these animals 

 the intimate contact of the food particles, absorbed within the 

 living substance, is aided bv the contractions of the sarcode, 

 by the emission and retraction of the pseudopodia. The 

 sarcode of these organisms absorbs nutrient matter from the 

 food particles. There is no distinct channel through which 

 the food particles pass. What causes the sarcode to absorb 

 nutrient matter from the heterogeneous materials introduced 

 into the cells by the pseudopodia ? There is no doubt that 



