THE FERTILIZATION-PROCESS 



each carrying a separate aster. This configuration, the 

 sperm-amphiaster, together with the sperm-nucleus comes to 

 lie near the centre of the egg. During this change in loca- 

 tion the small solidly staining sperm-nucleus becomes con- 

 verted into a lightly staining larger mass. In other words, 

 the compact mass of chromatin composing the sperm- 

 nucleus is resolved into diffuse faintly staining threads. 



The exact origin of the sperm-centrosome (centriole) is 

 not known. According to Mead,^ 



The behavior of the sperm-centrosomes is in harmony 

 with Boveri's theory of fertilization, but is not necessarily 

 a confirmation of it; for the karyokinetic activities which 

 are revived upon the entrance of the sperm are those 

 leading to the formation of the polar globules. The machin- 

 ery for these mitotic divisions is already organized, and it 

 is quite as likely that the stimulus which starts it going 

 emanates from the sperm-nucleus as that it emanates 

 from the sperm-centrosomes. 



The sperm-amphiaster develops into the cleavage-amphi- 

 aster. 



The eggs of Amphioxus — Class 3 — are laid toward eve- 

 ning during the breeding season of this animal. If sexually 

 mature animals are removed from the sea-sand, in which 

 they live, to clean sea-water, they will deposit their eggs.^ 

 Both Sobotta and Cerfontaine^ confirm an old observation 

 to the effect that these eggs develop best when shed into 

 sea-water already containing spermatozoa; if they lie in 

 sea-water before spermatozoa are added, they are suscep- 

 tible to polyspermy and develop abnormally. The eggs 

 form the first polar body while in the body of the female 



I Mead, 1S9S. 



~ Lwoff, 1 8^2, reported that he was able several times during the 

 season at Naples to obtain eggs and spermatozoa shed in the labora- 

 tory. On two occasions during i()2g I was able to induce animals 

 to shed. 



^ Sobotta, I.e.; Cerfontaine, I.e. 



167 



