GENERAL HISTOLOGY. 



97 



greater quantity, and therefore causes the greater dimen- 

 sions of the egg, according to the length of time during 

 which the egg is cut off from any other supply of nourish- 

 ment. We find the largest eggs in general in the case 

 of the highly organized oviparous animals, where a long- 

 continued course of development is necessary to lay the 

 foundation of the manifold organs. Besides the formative 



FlG. 34. Various spermatozoa, a, of the night-hawk ; ft, of the green frog ; y, of the cray- 

 fish ; 8, of a crab ; e, of the round worm (Ascaris) ; n, nucleus ; ;, middle piece ; j, fla- 

 gellum ; k, homogeneous body. 



yolk (protoplasm) and food-yolk (deutoplasm), there is 

 always found in the egg the cell-nucleus or the germinal 

 vesicle sometimes to be seen in large eggs even by the 

 unaided eye surrounded by a firm membrane. Its con- 

 tents are mainly the nuclear sap, through which is distrib- 

 uted an achromatic network, and in addition the nuclear 

 corpuscle, or nucleolus, called also after the discoverer the 

 Wagnerian spot, or the germinal spot. Often there are 

 multinucleolated germinal vesicles, especially in eggs which 

 contain very much yolk. 



