■iTO " ZOOLOGY. 



into the cloaca. In the sahimanders the end of the oviduct 

 serves as a uterus. Tliore are also fat-bodies (Fig. 433) at- 

 tached to the anterior end of the reproductive glands of the 

 toads and frogs, the use of which is unknown. For a gene- 

 ral idea of the structure of Amphibians the student should 

 dissect a frog or toad in connection with the following de- 

 scription and accompanying illustration (Fig. 433), prepared 

 by Dr. C. S. Minot. 



The frog is one of the types of Vertebrates most valuable 

 to the student, being readily obtained and easily dissected. 

 The accompanying figure represents the anatomy of the 

 spotted or leopard frog, Rana halecina, male. 



The skin is smooth, having neither scales, feathers, nor 

 hairs, and contains numerous microscopic glands, of which 

 there are said to be two kinds — one having an acid, the other 

 an alkaline secretion (L. Hermann). It is pigmented on 

 the dorsal surface, but whitish underneath. The head is 

 broad, triangular, with two large nasal oj)enings in front, 

 large and prominent eyes, two tympanic membranes formed 

 by a part of the integument stretched across a hard ring, 

 and an enormous mouth. The neck is short and not con- 

 stricted. The body tapers slightly posteriorly, and has the 

 opening of the cloaca upon the posterior end of its back. 

 Each limb consists of the three divisions : in the front leg, 

 irachium, antebraclmmi, and manus with four digits, of 

 which the fourth is very much thickened in the m,ale j the 

 sexes may be distinguished by this mark. In the hind leg 

 the three divisions are the femur, cms, and pes, with five 

 long digits, between which the membranous web is stretched. 

 If the web is examined in a living frog with a microscope, 

 the circulation of the blood in the capillaries can be studied. 

 The current of corpuscles and plasma is constant, and in a 

 given vessel passes only in one direction ; by following the 

 stream backwards and forwards it will be found to issue 

 from larger vessels, the arteries, and to enter into other and 

 different vessels, the veins. The pigment corpuscles can 

 also be seen in the web ; they are branching bodies, capable 

 of drawing in or expanding their processes, and they can be 

 made to contract by an electrical shock from an induction 

 apparatus. 



