II. II] 



Ch 



POLAR BODIES AND FERTILIZATION 



17 









produced by the filling and emptying of the lungs, and by the 

 movements of the heart. 



Swammerdam's account in 1737 describes the passage of the 

 egg from the ovaries to the oviducts by way of the ccelomic 

 space. Spallanzani in 1785 observed that the females of Bufo 

 igneus, isolated before union with the male, could still lay their 

 eggs. One of the tree-frogs has its eggs in the uterus before 

 it unites with the male. On the other hand, Spallanzani stated 

 that females of the stinking toad if isolated while the eggs are 

 still in the ovaries will retain their eggs, but if separated after 

 having paired will then deposit their eggs. According to the 

 evidence of several authors, Rana temporaria when isolated will, 

 in certain cases at least, set free its eggs. 



It has been suggested that the embrace of the male is me- 

 chanically necessary in order that the eggs may pass from the 

 ovary into the oviducts, 

 but this is certainly not 

 always the case, and if 

 not necessary in one form 

 is probably not necessary 

 in others. The sexual 

 excitement set up by the 

 tight embrace of the male 

 may however be neces- 

 sary in some species for 

 the successful perform- 

 ance of egg-laying. The 

 eggs pass one by one 

 down the length of the 

 oviducts, ultimately to 

 reach the lower portion 



of the tube, the so-called uterus, where the eggs accumulate. 

 If a frog is killed at the height of the breeding season, free 

 eggs are often found in the body-cavity, and a series of eggs 

 passing individually down the ovarian tubes, as well as an 

 accumulation of eggs in the uteri. In their passage through 

 the oviducts the eggs undergo certain internal changes and re- 

 ceive also their egg-coats. In the tubes of the oviducts the nu- 

 clear spindle divides, so that half of the original chromatin goes 



A 



Fig. 10. —Egg iu jelly. (After Schultze.) 



