SYNGAMY 



241 



When the spermatozoon arrives at the surface of the cone it is immediately 

 engulfed and passes deeper into the egg. The cytoplasmic granules at the 

 base of the cone disappear, leaving a hyaline pathway along which the 

 sperm head glides. Other spermatozoa being drawn through the jelly are 

 usually dropped by the retracting filaments when the first sperm enters 

 the egg; in case they do reach the egg surface they are stopped by the 

 fertilization membrane (Chambers, 1922c, 19236, 1930c). 



The most striking feature in both of these cases is the relatively 

 passive role played by the spermatozoon. Instead of actively forcing its 

 way into the egg by its own power, it is "swallowed" by the egg after its 

 own movements have ceased. In this connection Bowen (1923, 1924a6) 



^i'..Vov^ ^^oi^'^'i'^!^'^'^ Ci5^ii5r^^fc^l-^s^^ 



f f. C*'n j^"^ ^..*<. . 



2'30" 





2'33" 



2'34" 



2 '40" 



Fig. 146. — The entrance of the spermatozoon into the egg of the starfish, 

 occupied by the process is indicated. {After Chambers, 19236.) 



The time 



has advanced the view that the acrosome with its perforatorium is not 

 primarily a cutting tool but "essentially a secretory product the principal 

 function of which is to initiate the physico-chemical reactions of fertiliza- 

 tion. " The spermatozoon may show no such movements as would be 

 necessary for the use of a cutting or boring tool, and in some animals the 

 acrosome is neither of the right shape nor properly located to act in such a 

 capacity. In other animals, however, boring movements do occur. 

 Probably a pointed perforatorium is advantageous in either active or 

 passive movement through the jelly and egg membrane. 



K fertilization membrane is commonly formed as a result of fertilization. 

 In the echinoderm it first appears at the point where the spermatozoon is 

 attached and spreads over the egg with great rapidity. This really 

 consists in the elevation of a delicate vitelline membrane already present. 



