264 ANIMAL AGGREGATIONS 



the relatively greater activity shown under these conditions, as 

 Gemmil thought ; however, it is doubtful whether longevity is related 

 to the dilution of the nutritive fluid, which Gemmil supposed to be 

 the main factor involved. 



It is unnecessary to follow here the details of our advance in 

 knowledge concerning the mass relations of spermatozoa. The im- 

 portance the subject came to occupy may be realized by the fact that 

 in 191 5 Glaser, as Schiicking had done earlier (1903), questioned 

 whether a single spermatozoon was capable of initiating develop- 

 ment of a single egg, even though only one sperm nucleus is con- 

 cerned in the biparental inheritance. To explain these relation- 

 ships Glaser postulated a mass effect of spermatozoa, as well as an 

 individual effect. Lillie (19 19), reviewing his own earlier work on 

 this question, states that he can demonstrate that mass effect is not 

 necessary if the sperm suspensions have recently been made, and 

 that "the appearance observed by Schiicking and Glaser is found only 

 with suspensions not perfectly fresh." 



Lillie reports that fertihzing power of perfectly fresh sea-urchin 

 sperm may extend to 1/90,000,000 of i per cent, although at a dilu- 

 tion of 1/10,000 per cent one can rarely find a spermatozoon in the 

 jelly of the fertilized eggs. He states further, "If one determines by 

 comparison the rate of loss of fertilizing power of sperm suspensions 

 of different concentrations it is found that sperm suspensions of 

 1/240,000 per cent decline to zero in their fertilizing power in about 

 six minutes, those of 1/30,000 per cent in about fifteen minutes, 

 those of 1/300 per cent not until after more than two hours, while 

 one per cent sperm may retain their fertilizing power for two or 

 more days."^ 



The rate of loss of fertilizing power of fresh Arbacia sperm in 



' In nature the sperm of the sea urchin, Arbacia, used in many of these studies, are 

 shed from the genital pores into the sea-water, where they fertilize the eggs which have 

 been similarly shed by the females. In making sperm suspensions for such work as re- 

 corded here, the sea urchin is cut around the peristome and placed aboral side down. 

 The sperm is then collected in a clean, dry watch glass. Such sperm is designated "dry" 

 sperm and may be diluted as desired by adding the appropriate amount of sea-water. 

 Thus a I per cent suspension is made by adding i drop of sperm to 99 drops of sea- 

 water. 



