210 THE FROG CHAP. 



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 endoderm with the exception of the notochord, viz., 

 the connective-tissue, cartilage, bone, striped and un- 

 striped 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 preservative 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, and 61.) 



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-solution, and notice the form and movements of the 

 sperms (Fig. 62, B). Sketch. 



