334 MYRA MELISSA SAMPSON. 



sperm receptors are released more readily in specific egg-water, 

 filtrates of sperm suspensions in egg-water may evince greater 

 activating power than a combination consisting of a sperm 

 filtrate and filtered egg-water. Tests gave no indication of any 

 difference between them. It is also possible, as suggested by 

 Lillie (1915), that other substances are extracted from sperm 

 which may tend to neutralize the activating substances released 

 by them. 



There is abundant evidence that the sperm in contact with 

 mature ova, or secretions of ova, of the same species undergo 

 changes which are essential for fertilization. Their metabolism 

 is increased as indicated by their increased motility; their 

 chemical composition is changed as indicated . by decrease in 

 refringibility, by swelling of the sperm head, by changes in 

 viscosity, and by surface changes which permit agglutination to 

 occur. Spermatozoa may enter unripe eggs which lack "fer- 

 tilizin" or mature eggs from which it has been removed experi- 

 mentally but the sperm are not changed and they do not activate 

 the eggs. 



It is significant that in order for fertilization to occur these 

 essential changes in the spermatozoon must be produced when the 

 latter is in close proximity to an ovum. Sperm which have received 

 a long exposure to sea-water or a brief exposure to egg-water 

 are active and may surround or even enter ova of the same 

 species, yet fail to fertilize them. This loss of fertilizing capacity, 

 the transitory nature of agglutination, and the inability to obtain 

 a second agglutination reaction with sperm are indications of a 

 loss of substances essential in fertilization. To effect perfect 

 development such substances must be concentrated at the surface 

 of the sperm head at the instant when the latter comes into contact 

 with an ovum. Under such conditions they may initiate a chain 

 of chemical reactions, starting in the cortex of the ovum and 

 eventually involving all parts of the protoplasm of the egg 

 i.e., they may activate "fertilizin." If released into sea-water 

 or egg-water normally, or under the experimental conditions of 

 filtration and dialysis, these substances may be unable to produce 

 complete activation of ova of the same species, because of 

 dilution, instability, or neutralization by other substances elinii- 



