284 CARL R. MOORE. 



bodies in the cytoplasm of the egg. 1 Still other sections exhibit a 

 different type of reaction of the sperm to its new environment, 

 that appears significant the sperm heads may undergo swelling 

 and vacuolization without any indication of the appearance of a 

 sperm aster. For the most part asters arise only in connection 

 with a spermatozoon that shortly appears to be in the swollen, 

 rounded, and slightly vacuolated condition but, as has been 

 mentioned, some possess much more pronounced astral rays than 

 others. This condition of the entire absence of a sperm-aster 

 from the spermatozoon undergoing the more or less character- 

 istic changes of activity, probably to be referred to chemical 

 influences exerted upon it by some substance within the egg, 

 seems to indicate a quantitative reaction of the spermatozoon 

 with the egg, the sperm aster formation being the more sensitive 

 factor. In fact this series of preparations exhibits a gradient 

 of the effects of a spermatozoon, from essentially its normal 

 effect, to a condition in which it provokes not the slightest change; 

 and since a sperm aster is usually associated with a swollen 

 sperm head cannot this be an indication of the suppression of 

 sperm aster formation but a continuation of the more stable 

 changes accompanying sperm activity? 



(a) Penetration of the Spermatozoon. An interesting condition 

 for the observation of sperm entrance is presented by this series 

 of preparations and since the writer knows of no observations 

 on sperm entrance in Arbacia some passing mention of it may be 

 of interest. As may be seen from Fig. 4, two spermatozoa are 

 in the act of entering an egg and many other such sections are 

 to be found among the series. The egg has produced a small 

 protrusion of protoplasm as an entrance cone that projects 

 slightly above the egg surface; and within this cone lies the 

 sperm head pulled out into a narrow chromatin band, one end 

 of which projects down into the cytoplasm. No definitely formed 

 fixation body, to which the inner end of the spermatozoon is 

 attached, has been observed but the very shape and character 

 of the entering spermatozoon would indicate a decided attraction 

 from within the egg that acts upon the sperm head. 



1 Normal sperm asters appear within five to ten minutes. Around most of the 

 sperm heads is a small clear area produced by the retreat of protoplasmic granules 

 of the egg from its periphery. 



