414 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



and still more especially in the visceral cavities, are 

 found glands. We have already spoken of those of the 

 mesentery in connection with the lacteals. 



Function of the Glands.— The functions of these 

 glands are (i) to furnish leucocytes to the blood. We have 

 already spoken of this function in connection with the 

 mesenteric glands, but now add that all the lymphatic 

 glands have this important function. (2) They also, as 

 already seen in the case of the mesenteric glands, seem 

 to confer upon the lymph, and upon the blood, perhaps 

 through the presence of the leucocytes, the property of 

 coagulation. (3) They seem also to have the power to 

 arrest poisons on their way to the blood. The lymphatic 

 vessels seem to absorb everything. They absorb also 

 poisons. Such absorbed poisons are arrested in the 

 glands, producing inflammation and suppuration espe- 

 cially in the armpit and groin. The poison is thus elimi- 

 nated, and the patient saved. They suffer vicariously 

 to save the body. 



Comparative Morphology of the Lymphatic 

 System. — This system is found only in vertebrates. The 

 distinctive functions of the two systems — blood system 

 and lymph system — have not yet been differentiated in 

 invertebrates. The blood system performs the func- 

 tions of both. 



In lower vertebrates the lymphatic vessels become 

 much more distinct than in man ; and in amphibians — 

 e. g., in frogs — we find even propelling organs, lymphatic 

 hearts. Two of these are found in the sacral region and 

 two in the scapular region. They are also found in 

 some birds, especially in the embryo of birds. These 

 vessels empty into the blood system in various places. 



The lymphatic glands seem to appear first in birds, or 

 perhaps in Crocodilia. 



Mammals in this regard are in all respects like man. 



