334 COMPARATIVE MORPHOLOGY OF VERTEBRATES 



tures. Under this name are included two kinds of structures, the 

 pharyngeal and the palatine tonsils. The first of these lie in the 

 roof of the gullet, the palatine being situated between the inner ends 

 of the Eustachian tubes of amniotes, in mammals on either side of 

 the pillars of the fauces. Besides these there are lingual tonsils at 

 the sides of the roots of the tongue, and other similar structures at 

 various points of the floor and roof of the tetrapoda, concerning 

 which our knowledge is scanty. 



The haemolymph glands differ from the true lymph glands in the 

 presence of red blood corpuscles. Their function is supposed to be 

 somewhat the same as that of the spleen — the destruction of the 

 red blood corpuscles, and possibly the formation of both leucocytes 

 and erythrocytes. This latter type is rather uncommon, being 

 largely confined to the neighborhood of the aorta and its chief 

 branches, and to that of the postcava. 



Mention should be made of other possibly lymph structures. 

 Among these are the fat bodies (corpora adiposa) — band-like (uro- 

 dele) or lobulated, richly vascularized masses of fat (anura) connected 

 with the gonads of the amphibia. Of their origin and function Uttle 

 is accurately known. They are usually stated to arise from a 

 modification of the wall of the postcava, but lately they have been 

 said to come from the same general mass as the gonads themselves. 

 It is suggested that they prepare some substance for the gonads, a 

 view in accord with the fact that they are greatly reduced in the 

 spring of the year. Even less is known of the hibernating glands of 

 rodents and insectivores, masses of fat with (for fat) a very rich 

 blood supply. / 



y THE UROGENITAL SYSTEM 



In several phyla of the animal kingdom there is an intimate rela- 

 tion between the reproductive and excretory organs, the ducts of the 

 latter serving either to carry the products of the gonads directly to 

 the exterior or acting as brood organs where a portion of the develop- 

 ment of the egg takes place. This association of the two systems is 

 especially intimate in most vertebrates and hence this section is 

 headed Urogenital System, because of the difficulty of treating the 

 two components separately. 



The urinary or excretory organs have for their purpose the elimi- 

 nation of the nitrogenous waste (and occasionally other products) 

 from the system. They are paired organs which consist of glandular 



