GENERAL lUSTOLOGV. 



81 



gninules or polygoiiul bodies, tho )'olk-granules. Its quantity, 

 and thereforu the size of the egg, is in part proportional to tlie 

 length of time which tho 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 develoi)meut 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 additi(.)n the luicleolus, oalled also 

 the gennindl spuL 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. o'l, 



a and /i). Easiest to recognize in them is tlie head, which from. 



a y3 



Fig. 36— Various spermatozoa. «, of tho Tii,i.'lLt-hawk; P, of tlio j,'ropn frof,'; y, "f tho 

 crayflsh ; 6, of a crab; e, of the round worm [Afcarisl. ;i, nueh-us; in, middle 

 piece ; .s, fla^'ellum ; /,", homogeneous body. 



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

 renders possible the specific determination of the spermatozoa. 

 The heatl is the closely compacted chronuitic part of the nuidcus, 

 and henco colors very deeply in staining fluids. Xext comes an 



