PHYSIOLOGY OF THE INVERTEBRATA. 123 



mesenteries — are absorbed by the pseudo-haemal vessels, as 

 well as by the various tissues, &c., suspended in the peri- 

 visceral cavity. 



The Myeiapoda and Insecta. 



In these two classes of the Inmrtehrata there is a distinct 

 advance, in the mode of absorption, on all the forms alluded 

 to in the present chapter. 



Over the external surface of the alimentary canal there are 

 distributed blood-vessels ; and the nutrient matter of the food 

 is chiefly absorbed by these vessels, and more especially by 

 those carrying venous blood. Here the digested food is 

 absorbed by distinct vessels, although there may be some 

 transudation directly into the somatic or body cavity, 

 especially in some of the lower orders of these two classes. 



The vessels which absorb the digested food are not special 

 vessels (like the lymphatics of the Vertebratd) set apart for 

 the function of absorption, for they perform the ordinary func- 

 tion of veins, as well as " carrying away from the tissues of the 

 alimentary canal the effete products resulting from the work 

 of those tissues. But in addition to this there is laid upon 

 them the office of receiving the fresh material introduced into 

 the system through the alimentary canal. These vessels are 

 not only transmitting blood, but are absorbing ' chyle ' ; there 

 is a fusion of the functions of absorption and circulation." 



The Arachnida. 



The function of absorption in this class is j)erformed in a 

 similar manner to that of the Myriapoda and Insecta. The 

 digested food passes into the veins, and is conveyed to the 

 dorsal vasiform heart. 



The Crustacea. 



The digested food passes from the intestine into the blood- 

 vessels or veins, which are distributed on its walls. No other 



