ABSORPTION. 251 



by the lymphatics. None of the invertebrata, indeed, pos- 

 sess lymphatics, and absorption must consequently be per- 

 formed by the veins, when these latter vessels exist. The 

 addition of the system of lymphatic vessels, as auxiliaries to 

 the veins, may therefore be regarded as a refinement in or- 

 ganization, peculiar to the higher classes of animals.* 



Professor Muller, of Bonn, has lately discovered that the 

 frog, and several other amphibious animals, are provided 

 with large receptacles for the lymph, situated immediately 

 under the skin, and exhibiting distinct and regular pulsa- 

 tions, like the heart. The use of these lymphatic hearts, 

 as they may be called, is evidently to propel the lymph in 

 its proper course along the lymphatic vessels. In the frog 

 four of these organs have been found; the two posterior 

 hearts being situated behind the joint of the hip, and the 

 two anterior ones on each side of the transverse process of 

 the third vertebra, and under the posterior extremity of the 

 scapula. The pulsations of these lymphatic hearts do not 

 correspond with those of the sanguiferous heart; nor do those 

 of the right and left sides take place at the same times, but 

 they often alternate in an irregular manner. Professor 

 Muller has discovered similar organs in the toad, the sala- 

 mander, and the green lizard, and thinks it probable that 

 they exist in all the amphibia.f 



In Fig. 378. They correspond in structure, and probably also in their func- 

 tions, to the mesenteric glands, through which, in the mammalia, the lacteals 

 pass, before reaching the thoracic duct. It is chiefly in the mammalia, in- 

 deed, that these glands are met with; for they are rare among birds, and still 

 more so among fishes and reptiles. 



* Fohmann, who has made extensive researches on the absorbent vessels 

 throughout all the classes of vertebrated animals, has found that they termi- 

 nate extensively in the veins. See his work, entitled " Anatomische Unter- 

 suchungen uber die Verbindung der Saugadern mit den Venen." 



f Phil. Trans, for 1833, p. 89. 



