2i 4 THE BIOLOGY OF THE FROG CHAP. 



the body cavity near the base of the lung. At the posterior 

 end it enlarges to form the thin-walled, very distensible uterus; 

 the openings of the two uteri lie close together on the dorsal 

 wall of the cloaca. With the exception of the uterus, and 

 a short space at the anterior end, the oviducts possess a thick 

 glandular wall. The inner surface of the oviduct is thrown 

 into longitudinal ridges, which are covered with ciliated 

 epithelium. The grooves between the ridges receive the 

 openings of the numerous glands which secrete the gelati- 

 nous coats of the eggs. These glands are mostly of the 

 simple tubular type ; they are lined by a single layer of 

 cylindrical secreting cells which become very much enlarged 

 during the breeding season. When the secretion is dis- 

 charged, the outer membrane of the cells is burst (Lebrun), 

 and the contents, which formed a greater part of the bulk 

 of the cell, flow into the lumen of the gland. After the 

 discharge of the secretion the glands become very much 

 reduced in size, and the whole oviduct much thinner, and of 

 a yellowish color from the accumulation of fat. As Boett- 

 cher has shown, the oviducts in the breeding period possess 

 a remarkable capacity for the absorption of water. A pair 

 of oviducts, which when just taken out of the body weighed 

 9.6 g., were found to weigh 1084 g. after they had lain some 

 time in water; i.e. they had increased in weight 113 times. 

 After the breeding season this power of absorbing water is 

 very much reduced. The eggs, as they are discharged from 

 the ovaries, are taken into the mouths of the oviducts by means 

 of ciliary action. They are then carried down the oviducts by 

 means of the cilia on the ridges of the inner walls. During 

 this passage they receive their coats of jelly, after which they 

 collect in the uteri, whose walls they greatly distend. Here 

 they may remain for several days, the length of time depend- 

 ing upon the presence or absence of the male (see p. 51). 



