SPERM FILTRATES AND DIALYZATES. 335 



nated or extracted from sperm. They may, however, produce 

 changes in the surface of the ovum which facilitate its reaction 

 with a spermatozoon. These changes may account, in part, for 

 polyspermy when ova are inseminated with an excess of fresh 

 sperm and for the effectiveness of stale sperm if concentrated 

 suspensions are used. Such substances may account for the 

 antagonistic effect produced by sperm of one species on those of 

 another; and for the neutralizing effect of concentrated sperm 

 suspensions on the action of blood serum. 



IX. SUMMARY. 



1. Solutions obtained by filtration and dialysis of suspensions 

 of living sperm in sea-water activate ova of the same species. 



2. Tests indicate that the effect is produced by some substance 

 derived from the sperm, and not by some extraneous partheno- 

 genetic factor. 



3. Ova of Nereis exposed to specific sperm filtrates form 

 fertilization membranes, complete their maturation and some 

 develop into abnormal trochophores. Ova of sea-urchins fail to 

 form membranes but do undergo nuclear and cell division. 



4. Ova exposed to filtrates and dialyzates are rendered more 

 susceptible to the action of hypertonic sea-water, and to the 

 entrance of sperm. 



5. In normal fertilization sperm exposed to " fertilizin " undergo 

 profound modification in chemical structure and organization; 

 and unless such modification occurs the sperm fail to fertilize 

 the egg, even though they may enter it. It is possible that sub- 

 stances localized in the surface of the sperm head activate the 

 ovum. Such localization is transitory. 



6. Such substances, when given off by sperm into sea-water or 

 egg-water, either because of dilution, decomposition, or admixture 

 with waste products given off by sperm, produce definite changes 

 in such ova, but are unable to effect complete activation of ova 

 of the same species. 



LITERATURE. 

 Blount, M. 



'09 The Early Development of the Pigeon's Egg, with Special Reference to 

 Polyspermy and the Origin of the Periblast Nuclei. J. Morph., 22, 1-64. 

 Chambers, Robert, Jr. 



'23 The Mechanism of the Entrance of Sperm into the Starfish Egg. J. Gen. 

 Physiol., 5, 821-29. 



