64 



MYRIAPODA 



parent cell from which it is derived ; each of these cells has, like 

 the parent cell, the same property of dividing into two more, and 

 so on. Thus from this continual process of division or reproduc- 

 tion of every living cell, the materials are provided for the 

 building up of the body. 



The regularity of the process of the division of the ovum, or, 

 as it is called, segmentation of the ovum, is interfered with by 

 the presence of food yolh. The cells formed by the process of 

 cell division just described need nourishment, and this nourish- 

 ment is supplied to them by the food yolk formed in the body 

 of the ovum before the process of segmentation begins. It is 

 easy to understand that this yolk, which is not alive like the 



y.sj 



Fig. 37. — Later stage: nv, 

 nucleolus ; c.j), nucleus ; 

 y.sp, yolk spherules ; ch, 

 shell. 



m« 



cells, cannot divide like them, and therefore the segmentation of 

 the ovum in Myriapods is irregular, as it is called. 



I will now go back a little and describe what happens to the 

 ovum before the process of segmentation is complete. It increases 

 in size and forms the supply of food yolk which is to provide the 

 nutriment of the ovum. Then after impregnation the egg-shell 

 is formed round it, and it becomes what we know as the egg. 

 This egg is not a perfect sphere, but is oval (in most Myriapods) 

 in shape. The egg is laid, and the process of segmentation begins 

 shortly after it is laid, as has already been described. 



When it has been laid for about 36 hours, if we take an egg 

 and, after proper preparation, cut it into thin slices known to 



