^lATUKATIOX OF THE EGr-f. 9 



Concerning the real nature and significance of tlie changes 

 described above there has been much discussion, and the matter 



Fig. 1. — ^Successive stages in the maturation of the eL'-g" of the Fro^^ The 

 eggs are represented as bisected vertically. .-- 25. (After 0. Schultze.) 



A> stage ID ■\vliichtbenuclensbascommenced to shrink, ami the nuclear skein isforme-l 

 in its centre. B, statje in whicti the nuclear skein has naoved to the surface of the egg", 

 just prior to formation of the first polar body. C> ^^■^'^'^ in \v]iich the first polar body- 

 has been formed, by division of the nuclear skein, and extnided. D, stage in which the 

 second polar body has been extrudeil, and tljc remaining yiart of the nuclear skein, or 

 female proniicleus, has retreated from the surface of the egg and is about to unite with 

 the male pronucleus, or hearl of the spermatozoon. 



PB, first I'tolar body. PB'. second polar body. TJF, female pronucleus. TJG-, egg 

 nucleus, or germinal vesicle. TTTT, fl^iid esuded frum germinal ^x-icle. XJ3VL. male 

 pronucleus. Z, vitelline membrane. 



is not vet thoroughly understood. The points of chief impor- 

 tance appear to be the following. 



1. The process of maturation concerns the egg alone. It 



