PHYSIOLOGY OF THE IXVERTEBRATA. 137 



parable to spontaneous coagulation. The substance which 

 becomes brown in air does not form any intermediate vehicle 

 between the exterior air and the tissues which require it. 

 The existence of such an intermediate vehicle is most 

 doubtful, especially when one bears in mind the anatomical 

 disposition of the respiratory apparatus in the Insccta^ i.e., 

 the air penetrates by the trachea? among all the living tissues. 

 By means of the tracheas the function of respiration is carried 

 on in every part of the body. 



The Crustacea. 



Dr. Leon Fredericq* has examined the blood of various 

 Cnistacm. The blood of crabs, lobsters, &c., which live in the 

 sea, has exactly the same taste as sea water ; which leads 

 one to suppose that the blood or nourishing fluid of these 

 animals has the same saline composition as the waters in 

 which they live. 



According to an analysis of Backs, and cited by Pelouze 

 and Fremy,t the water of the North Sea contains a little 

 more than three per cent, of soluble salts : — 



3.046 



It tastes strongly salt and bitter. 



In support of the idea that the blood of certain Crust((cr/( 

 living in the North Sea, has the same saline composition as 

 the medium in which they live, Fredericq obtained the 

 following result after analysing the blood of an Ostend 

 lobster (Homarus vulgaris) : — 



3.040 per cent, of soluble ashes. 



* BiiVt't'nia (If rjcatlemie Jfoi/n'e ilc Btlf/ique, 2" serie, tome iv. 

 t Tiuite dc C'himte, y 6d., tome i, p. 252. 



