50 THE BIOLOGY OF THE FROG chap. 



over masses of eggs. The supernumerary males, therefore, 

 play a part in fertilizing the eggs, as well as those which 

 have succeeded in obtaining a mate. 



What the stimulus is that prompts the male to discharge 

 his sperm at the same time the eggs are extruded from the 

 female is not altogether evident ; the same problem presents 

 itself in the case of fishes. 



Congreg-ating at Breeding Grounds. — During the breed- 

 ing season frogs usually congregate at certain points in shal- 

 low water in considerable numbers. At this time there 

 seems to be manifested a gregariousness which does not 

 appear under ordinary circumstances, and which is not 

 entirely accounted for by the tendency of the animals to 

 seek a similar habitat for breeding. According to Fischer- 

 Sigvvart's observations on Rana fusca, if only a few pairs 

 occur in any locality, they get as closely together as possible, 

 and their egg masses form almost a continuous sheet. The 

 laying grounds are the scenes of lively activity, " Alles hastet 

 und drangt." The supernumerary males crawl over and 

 work through the masses of eggs and, according to Fischer- 

 Sigwart, effect the fertilization of the ova which may not 

 have been reached by spermatozoa at the time of their 

 discharge. 



When the sexual products are discharged, the frogs go 

 back upon the land and scatter in all directions. Most 

 frogs leave the breeding grounds at nearly the same time. 

 At one day a place may be teeming with these creatures, 

 while on the following day not a single individual can be 

 found. Henceforth the frog is a solitary animal, having lost 

 all its sexual instincts and social proclivities. It leads its 

 life as if no other member of its species were in existence. 



Egg Laying without the Presence of the Male. — The 

 question whether or not the female frog will lay eggs without 



