266 ANIMAL AGGREGATIONS 



of motility alone, and declines more rapidly than does motility (F. 

 R. Lillie, 1915; Lillie and Just, 1924). Sperm may be injured in 

 such a way that its fertilizing power, as measured by the proportion 

 of eggs fertilized and the normality of cleavage and development, is 

 materially lessened while motility is not visibly impaired (Hinrichs, 

 1926; Lillie and Baskervill, 1922)." 



That such is the case is evidenced by one experiment reported by 

 Lillie (1915) and cited by Lillie and Just (1924) in which eggs were 

 added to a 1/2'° sperm suspension that was near the point of com- 

 plete loss of fertilizing ability. "The sperm were still active and 

 entered the jelly of the eggs to such an extent that in ten eggs 

 selected at random an average of nine spermatozoa was counted in 

 contact with each egg in optical section; the eggs, however, remained 

 unfertilized." 



Had fertilization occurred, and with slightly less stale sperm, as 

 there is a possibility that it might, we might perhaps be dealing 

 with mass fertilization, as suggested by Schucking and Glaser. On 

 a priori grounds, if the abihty of the sperm to initiate development 

 depends upon a material which leaches out before the loss of motil- 

 ity, then what one spermatozoon is unable to supply might be sup- 

 plied by many. Barthelmy (1923, 1926), in discussing polyspermy, 

 states that the egg reacts in proportion to the stimulus given by the 

 sperm, so that when this is weak, as in the case of aged sperm, the 

 egg reacts slowly and more sperm enter, producing polyspermy. Al- 

 though there is evidence that the defect in polyspermy is in the egg 

 rather than in the sperm, there is still a possibihty that the phenom- 

 enon of physiological polyspermy may also be an instance of the 

 same sort of mass fertilization behavior. Such polyspermy is charac- 

 teristic of forms with large eggs, such as sharks, some Amphibia, rep- 

 tiles, and birds. Insect eggs of several sorts are said to possess 

 more than one micropyle as a structural adaptation for polyspermy 

 (Henking, 1891). Lillie and Just state that among animals having 

 small eggs, physiological polyspermy occurs only in the Bryozoa, 

 where the sperm are united in bundles, and where the research 

 worker describing the phenomenon (Bonnevie, 1907) thinks that 

 polyspermy has definite value for the organism. Lillie and Just do 

 not accept her interpretation on this point. 



