210 THE FROG CHAP. 



formed the epiderm and the cutaneous glands ; the 

 whole of the nervous system, central and peripheral, and the 

 essential parts of the sensory organs, as well as the crystalline 

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

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

 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, mz., 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 ithe 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 will 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, and6i.) 



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

 of peritoneum connecting it with the corresponding kidney ; the efferent 

 ducts ; the branched fat-body \ the ureter (urinogenital duct}', and the 

 seminal vesicle. Sketch after examining the cloaca (see next page). 



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



