GENERAL HISTOLOGY. 



81 



granules or polygonal bodies, the yolk-granules. Its quantity, 

 and therefore the size of the egg, is in part proportional to the 

 length of time which the egg is cut off from any other supply of 

 nourishment. In general we find the largest eggs 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 protoplasm and deutoplasm, a cell 

 nucleus or germinal vesicle (sometimes visible to the naked eye) 

 surrounded by a membrane always occurs in the egg. Its contents 

 are mainly the nuclear fluid, through which is distributed an 

 achromatic network, and in addition the nucleolus, called also 

 the germinal spot. Often there are multinucleolated germinal 

 vesicles, especially in eggs which contain very much yolk. 



The Spermatozoa, the morphological elements of the male 



reproductive product, are so small that their finer structure can be 



studied only with the strongest powers of the microscope (fig. 36, 



a and /?). Easiest to recognize in them is the head, which from 



a J5 



FIG. 36 Various spermatozoa, a, of the night-hawk; 0, of the green frog; >, of tho 

 crayfish ; 6, of a crab ; e, of the round worm (Ascaris). n, nucleus ; w, middle 

 piece ; , flagellum ; 7c, homogeneous body. 



its variety of form spherical, oval, sickle-shaped, etc. often 

 renders possible the specific determination of the spermatozoa. 

 The head is the closely compacted chromatic* part of the nucleus, 

 and hence colors very deeply in staining fluids. Next comes an 



