ORGANS OF SECRETION. 599 



enclosing the mucous secretion, and they are supplied with 

 large branches from the fifth and eighth pairs of nerves. 

 The frequent excitement of the electrical organs appears to 

 exhaust rapidly the influence of the ganglionic nerves 

 of digestion and secretion, and to arrest these processes. 

 The highly vascular secreting organ, connected with the/ 

 parietes of the lungs of fishes, and which appears to 

 produce the gaseous contents of the air sac when destitute 

 of ductus pneumaticus, has been considered analogous to 

 the thymus gland of higher vertebrated classes, but it is here 

 a permanent and essential part of the pulmonary sac. 



From the aquatic habits and the imperfect masticating 

 powers of the amphibious animals, their salivary glands are 

 nearly as little required and as little developed, as in fishes 

 or in cetacea, but their buccal cavity, like the naked surface 

 of their skin, is abundantly provided with muciparous follicles, 

 and the whole course of their digestive canal. The liver, as 

 in fishes, is proportionately large and always provided with 

 a large gall-bladder, and it is partially divided into two lobes, 

 as in most reptiles. In the pipa there is a third intermediate 

 lobe, and they are more free, as in the chelonia. The liver 

 commences in the tadpole by a small pit or crypta on the 

 side of the intestine, like the concavity left in the adult 

 liver of many mollusca ; from this a few small simple short 

 follicles gradually extend ; these increase in number, elongate, 

 and divide to constitute at length the entire mass of the 

 adult organ. The pancreas is always conglomerate, as in the 

 plagiostome fishes, and opens into the duodenum beside the 

 biliary duct. The highly vascular spleen, is single as in 

 reptiles, of an elongated form like the stomach, and is 

 attached by cellular tissue and vessels along the left side of 

 that organ, as in higher vertebrata. The muciparous glands, 

 so largely developed and extensively ramified immediately 

 beneath the skin of fishes, assume a more divided form on 

 the naked skin of amphibia, where they pour out their viscid 

 and sometimes acrid secretion, by open pores dispersed over 

 all parts of the surface. The excretory orifices of these 

 cutaneous follicles are large and obvious over the back of 

 the land salamander, and their acrid product in the toad is 

 alkaline, not acid like most other excretions. The glandular 

 follicles which secrete this bitter, oily, and poisonous fluid 

 on the back of the toad, are chiefly disposed on the dorsal 



