2IO THE FROG chap. 



lens of the eye ; and also the epithelium lining the mouth 

 (stomodaeum) and outer part of the cloaca (proctodseum). 

 The endoderm gives rise to the epithelium lining the enteric 

 canal and its various offshoots, including the lungs, urinary 

 bladder, gastric glands, bile and pancreatic ducts, as well as 

 the glandular cells of the liver and pancreas ; and to the 

 notochord. From the mesoderm are developed the various 

 parts which are situated between the ectoderm and endo- 

 derm with the exception of the notochord, viz., the connec- 

 tive tissue, cartilage, bone, striped and unstriped muscles, 

 circulatory organs and peritoneum, as well as the urinary 

 and reproductive organs and the accessory parts of the 

 sensory organs. 



PRACTICAL DIRECTIONS. 

 Organs of Reproduction. 



Open a frog in the usual way : cut through the gullet, rectum, and 

 mesentery, and remove all the digestive organs. In the female take 

 especial care not to injure the roots of the lungs in severing the gullet. 

 One of the specimens you have already dissected and kept in the pre- 

 servative fluid should still contain the urinogenital organs intact in the 

 case of the male : in the female, the ovaries and greater part of the 

 oviducts v^ill have been removed, but the relations of the two ends of 

 each oviduct can still be made out. 



Examine the reproductive organs, which will now be freely exposed, 

 under water — or in the case of the female, in i per cent, salt solution. 



I. Male Organs. (Figs. 3, 5, 7 and 61.) 



1. Notice again the sperm aries or testes, each supported by a fold 

 of peritoneum connecting it with the corresponding kidney ; the efferent 

 ducts; \he htZ-Qchei fat-body ; the ureter (urinogenital duct) ; and the 

 seminal vesicle. Sketch after examining the cloaca (see below). 



2. Tease up a bit of the spermary of a recently-killed frog in salt 

 solution, and notice the form and movements of the sperms (Fig. 62, B). 

 Sketch. 



3. Examine under the microscope a transverse section of the spermary, 

 prepared as directed on p. 136, and note (Fig. 62, A) the numerous 



