196 



THE FROG 



CHAP. 



becomes covered with a delicate egg-membrane. By 

 the time the egg is mature a superficial deposit of 

 pigment takes place over one hemisphere. 



In the young condition all the epithelial cells forming 

 the walls of the ovary are alike, but as the organ 

 reaches maturity, certain of them (o) enlarge and give 



C.I 



FIG. 63. Transverse section of Frog's ovary. (X 30.) 



//. v. blood-vessels ; c. t. connective-tissue ; ep. outer layer, and ep' inner layer o( 

 epithelium; ep", outer layer of ovisar, continuous with ep' ; ep'" , K< mini il 

 epithelium, derived from ep. ; ep'"', folHcular epithelium, de-rived from ep. ; 

 nu. nucl 'u^ of ovum : nu', micleoli ; o. young ovum ; pr. protoplasm of ovum 

 containing yolk-granutes. (After Marshall.) 



rise to the ova, while others form an investment or 

 follicle (ep"") for each ovum. 



The oviduct (Fig. 4, /. ovd, r. ovd), as you have seen, 

 is a long and greatly convoluted tube lying above or 

 dorsal to the ovary. Its anterior end narrows consider- 

 ably, runs parallel with the gullet, passes to the outside 

 of the root of the lung, and then opens into the ccelome 

 by a small aperture (r. ovd'). The greater part of the 

 oviduct is about as wide as the small intestine, and is 

 thick-walled and lined with gland-cells, which secrete 



