Introduction to jilniinal Alorphology. 33 



The exposure to air takes place in the respiratory 

 organs, of which there are four types — ist. In aquatic 

 animals, the blood, contained in organs called branchiae 

 (gills), is exposed to water containing oxygen in 

 solution; 2nd. Also in water dwellers, a system of 

 tubes communicating with the external water and 

 traversing the animal's body, admits this fluid so 

 as (through their walls) to aerate the blood in the 

 perivisceral space (water vascular system) ; 3rd. A 

 system of tubes (tracheae) containing air, ramifying 

 through the body, whereby the blood may be directly 

 aerated ; or 4th. A series of sacs (pulmonary sacs, 

 lungs) set apart for the reception of air, to which the 

 impure blood is brought, and exposed in capillary 

 vessels.* 



The glandular depurants remove from the blood 

 the waste of nitrogenized material. They are the 

 dermal glandsf (the only ones in the lowest forms), 

 and kidneys. J 



* In the respiratory- organs, water, carbonic acid, and traces of other 

 substances are got rid of and oxygen taken in. As this oxygen enters into 

 chemical combination with the protoplasm in the tissues in the hfe 

 processes, in all living forms heat is evolved during such chemical 

 action, and the amount thereof varies with the activity of the com- 

 binations. 



t In the perspiration, or excretion of the dermal glands is contained 

 water, sodic chloride, ammonic lactate, butyrate, and acetate, some nitro- 

 genous materials, sometimes formic acid, and an odorous principle. 



% The kidney separates from the blood, urea, uric acid, often combined 

 with ammonia, kreatin and ki-eatinin, sometimes hippuric and benzoic acids, 

 xantliin and hypoxantliin, urophxin, and salts similar to those in blood 

 serum. 



D 



