248 INTRODUCTION TO CYTOLOGY 



somes divide but do not separate. Although the cytoplasm becomes 

 active, no cytokinesis ensues. The chromosomes then return to the 

 reticulate condition. This process is repeated several times, the nucleus 

 increasing in bulk each time, but it soon becomes very irregular and the 

 egg ultimately breaks down by general cytolysis. The second treatment 

 in some way gives the egg the capacity to divide regularly. Morgan 

 (1899) and Wilson had long before shown that such treatment with hyper- 

 tonic sea water causes aster formation in the unfertilized sea-urchin egg. 

 Herlant showed that one of these asters and a second aster formed near 

 the egg nucleus together form an amphiaster, normal division then 

 ensuing. Thus the breakdown of the egg after the first treatment alone 

 appears to be related to the absence of a proper coordination of nuclear 

 and cytoplasmic division. The second treatment produces a regula- 

 tory effect, partly through aster formation, this resulting in normal 

 development. 



Among other agencies inducing activation in certain cases may be 

 mentioned high temperature (R. S. Lillie, 1908, 1915; Heilbrunn, 1925a), 

 carbon dioxide (Herlant, 1920), puncture by needles, allowing gases or 

 other substances to pass the membrane (Bataillon, 1910, and others), and 

 release from the vitelline membrane (Heilbrunn, 19206). With respect 

 to the effect of heat, Heilbrunn (1925a) finds a measurable increase in 

 viscosity at temperatures inducing artificial parthenogenesis and reiterates 

 his theory (1915) that all such activating methods produce a gelation or 

 coagulation in the egg cytoplasm. 



F. R. Lillie (1913 et seq.) advanced the theory that the egg is an 

 "independently activable system," the spermatozoon contributing 

 neither organs nor substances necessary to activation. "The egg 

 possesses all substances needed for activation; the spermatozoon is an 

 inciting cause of those reactions within the egg system upon which devel- 

 opment depends." As a result of his direct analysis of the gametes during 

 the fertilization period, Lillie identified a substance in the egg which he 

 called fertilizin. This substance is present in the egg for a short time 

 only. Its formation usually begins at about the time of the breakdown 

 of the germinal vesicle, from which it probably emanates; immediately 

 after fertilization its production ceases. As a rule, it is only during the 

 brief period when fertilizin is present that spermatozoa will enter the 

 egg. Moreover, membraneless egg fragments without fertilizin are not 

 entered. Hence it seems clear that the entrance of more than one sperma- 

 tozoon is normally prevented, not simply by the mechanical barrier of the 

 fertilization membrane which develops when the first sperm enters, but 

 also by the physiological state of the egg protoplasm itself. 



Fertilizin has two effects: it first acts by causing an agglutination of 

 the spermatozoa at the surface of the egg, and later causes the activation 

 of the egg. It may thus be said to stand between the spermatozoon and 

 the activation reactions in the egg. Being present in the egg secretion 



