MATURATION OF THE EGG 



31 



cell nucleus, and a mobile filamentous appendage, the tail, which is of 



protoplasmic nature, and is much like the flagellum of the Flagellata. 



Besides the tail there may be accessory nagella. Between the head and 



the tail a special intermediate portion is sometimes interposed. Other 



forms of spermatozoa are occasionally 



found ; round, pear-shaped, etc., either /^ X* "^-w^^'^Nn I 



stationary or moving like Amcebcv. The ' 



spermatozoa arise in the testis from a 



germinal layer or epithelium, as do 



eggs. After repeated division of the 



original formative elements, cells are 



produced which are equivalent to egg 



germs, and which may be distinguished 



as sperm germs. Whereas, however, 



the egg germs become eggs direct by 



means of growth and maturation, the 



sperm germs are still further divided FIG. 27. various forms of sperma- 



and produce spermatozoa. We have J 0203 " Of Mwnmai ; a, of a Turbei- 



. lanan, with two accessory flagella ; c. d, 



already seen a phenomenon similar, an d e , of Nevada; /, of a crustacean; 



though not in all points parallel, in 9, of a Salamander (with undulating mem- 



i 



An Ordinary Cell Of the Colony brane );^ The commonest pin-shapedform. 



there becomes by growth a large egg, or by division a mass of small 

 spermatozoa. 



Maturation of the Egg. 



The ejection of the directive or polar bodies is the 'last stage in 

 the maturation of the egg which precedes fertilisation. The germinal 

 vesicle moves towards the surface of the egg (towards the animal pole 

 in the case of eggs differentiated into poles), and here undergoes 



kb 

 pn 

 nu 



... kf 

 kb 



FIG. 28. Disorganisation of the germinal vesicle and formation of the nuclear spindle in 

 eggs of Asterias glacialis, after O. Hertwig. x, Prominence of protoplasm ; Itf, germinal spot 

 which divides into two distinct substances, pn and nu ; fc&, germinal vesicle ; sp, nuclear spindle. 



considerable changes. It becomes partially disorganised (Fig. 28). 

 Out of part of its contents is formed that spindle-shaped figure 

 (Fig. 28, B) which is characteristic of indirect nuclear division (see 

 below, pp. 35,36). The one half of the spindle enters a small mass of 

 protoplasm which projects from the surface of the egg. This prominence 



