THE FERTILISATION OF THE EGG 11 



go on developing (so-called merogony). This was found by 

 Delage as early as 1899. All this shows that the mixing of 

 nuclear sap and cytoplasm at the beginning of maturation is 

 of great importance for fertilisation. 



In the fusion of e^g and sperm, substances secreted by each 

 of these cells play a major role (Hartmann, Schartau and 

 Wallenfels, 1940). In sea urchins, both gametes have been 

 shown to secrete two types of fertilisation substances, or 

 gamones. Gynogamone /, secreted by the eggs, accelerates the 

 movements of the sperms, and perhaps also attracts them so 

 that they reach the eggs more rapidly. Once the sperms have 

 reached the egg, they are "agglutinated" (made sticky) by 

 gynogamone II. This substance also paralyzes sperms of other 

 species, and thereby reduces the danger of hybrid fertilisation. 

 The sperms produce androgamone /, which slows down their 

 movements so that they are immobile in the male genital ducts, 

 and do not exhaust their energy too early. They also produce 

 androgamone II which dissolves the envelopes of the egg, and 

 counteracts the agglutinating action of gynogamone II, there- 

 by enabling the sperms to penetrate quickly into the egg. In 

 this way, the gamones, which are probably of common occur- 

 rence, ensure the normal course of the fertilisation process. 

 Investigations by Tyler (1948) have demonstrated that the 

 reaction between male and female gamones has a great similar- 

 ity to immunological reactions. In American literature both 

 gynogamones are grouped together under the name of ''ferti- 

 lizing, and both androgamones under the name of "anti- 

 fertilizin". 



The situation in mammals deserves special mention. When 

 leaving the ovary, the eggs of this group are surrounded by a 

 layer of cells, the cumulus oophorus. These originate from the 

 follicle. They are kept together by a viscous substance, probably 

 consisting mainly of hyaluronic acid, or a related polysaccha- 

 ride. Now it has been proved that the sperms contain an enzyme, 

 hyaluronidase, which breaks down hyaluronic acid, and thereby 

 causes the disintegration of the cumulus oophorus so that the 

 sperms gain free access to the egg surface. 



After the sperm has pierced the envelopes of the egg, and 



