ITS CHEMIC0-PHYS1CAL AND MORPHOLOGICAL PROPERTIES 53 



I have observed (IT. 19) that the germinal spot is composed of 

 two substances in Helix, Tellina, and Aster acanthion, as well as in 

 Anodon. Asteracanthion (Fig. 31) is of special interest, as the 

 separation into two substances (pn,nn) only becomes distinctly 

 visible when the germinal vesicle commences to break up and to 

 form the polar spindle out of its contents. 



Finally, in the description of the structure of the resting nucleus, 

 attention mast be drawn to one other important point. According to 

 the age or stage of development of a cell, the resting nucleus may present 

 very considerable variations in all its separate parts: as to the appearance 

 of its fram ework, and as to the number, size, and peculiarities of its nuc leoli. 

 Thus, as Flemming (II. 10) remarks, " In young eggs from the 

 ovaries of Lamellibranchs, this twofold composition of the large 

 nucleolus is not to be seen ; it only develops in the mature Qgg.^ 

 Above all, the germinal vesicles of the eggs undergo during their de- 

 velopment important metamor- 

 phoses, which at present have 

 been but little investigated, 



whilst their significance is still r : '. V'-r-"-" 



less understood. The same is 





Z pn } kf 



nn ) J 



true of the nuclei of sperm Y A 



mother cells. I have en- "%Cv ^ y -:^' 



deavoured to follow accurately '^iiri.e^ 1 *'' 



these changes of form in Such Fig. 31. Section from an egg of Asterias 



cells obtained from the testis of glacinlis showing the (le s en eration of the 



germinal vesicle. This begins to shrink up, 

 AscaHs megalocephala (II. 19 b), whilst a mass of radiated protoplasm (as) 



which are very suitable for the foices its way int0 the interior, breaking 



down the membrane. The germinal spot 

 purpose. ( fc yj is htill visible, but is divided into two 



As is shown in Fig. 32, form A substances, nuclein (mi) and paranuclein 

 ~. ^l n u j (p*0- (0 Hertwig, Embryology, Fig. 12.) 



gradually becomes transformed ' 



into form B, and this during the process of development of the 

 spermatozoon into form C ; the youngest sperm mother cells (B) 

 have naked nuclei containing dense nuclear frameworks, and 

 superficially-placed nucleoli ; this form develops in older cells (G) 

 into a vesicular nucleus with a distinctly marked membrane. In 

 the vesicle a few linin threads are extended through the nuclear 

 sap, the nuclein heaped up into one or two irregular masses, 

 amongst which the more or less globular nucleolus is situated. In 

 cells which are not yet mature, the nuclein is collected chiefly at 

 one spot of the nuclear membrane in the form of a thick layer, 

 whilst granules of varying size lie upon the surface of the linin 



