] THE FROG. 165 



The tail; in all probability beginning to shrink. 



/. The young frog shortly after the moult (shedding 

 of the larval skin): characterized by the coex- 

 istence of both pairs of limbs and the tail. 



Note its frog-like characters and especially 

 a. The mouth ; gape-wide, sucking lips gone, horny 



teeth replaced by true teeth. 

 ft. The tail ; absolutely shorter than in the late 



tadpole. Note its relations to the trunk, 

 y. The cloacal orifice. Examine this with care; 

 although displaced, owing to the increase in 

 size of the hind-limbs and their approximation 

 in the ventral middle line, it still lies at the 

 base of the tail (i.e. it is ventral in position. 

 Cf. the adult). 



ii. The formation of the embryonic layers and certain 

 of the more important organs. 



Imbed and cut sections of the preserved oosperm 

 or larvse, as directed below. Staining is unnecessary; 

 hsematoxylin may be used, if desired. 



a. At the first cleavage ; longitudinal and at right 

 angles to the cleavage furrow. 



a. The blastomeres ; equal in size and separated by 

 the cleavage furrow. Protoplasm ; densely pig- 

 mented above, little so below, for the most 

 part laden with yolk granules. 



j3. Nuclei. These may or may not be visible; 

 each is clear and transparent and generally sur- 

 rounded by pigment. (If visible, look for indi- 

 cations of division.) 



