8 



INTRODUCTION PEOTOPLASM CELL 



FlG. 7. P R I M A R Y 



SPERMATOCYTE OF 



A TURTLE (CiSTUDO 



CAROLINA). 



Showing chromatic 

 spherules ('chromidia') 

 apparently in process 

 of extrusion from the 

 nucleus. X 1500. 



known as 'deuteroplasm' (Studnicka). The endoplasm is commonly 

 described as consisting of a more fluid, finely granular ground substance, 

 the hyaloplasm (paraplasm, interfilar mass, para- 

 mitome, enchylema, cytolymph), containing a del- 

 icate denser reticulum, or cytoreticulum, with 

 polygonal or spheroidal meshes. The substance of 

 the reticulum is called spongioplasm (mitome; 

 filar mass). It is held by some to be continuous 

 with the linin mesh of the nucleus. The granules 

 of the ground substance, both free of and attached 

 to the spongioplasm, are called microsomes. Ac- 

 cording to one interpretation the spongioplasm 

 arises by coalescence of microsomes. A more re- 

 cent interpretation regards both network and 

 granule as simply more condensed portions of the 

 hyaloplasm. The cytoplasm may contain, besides 

 the aforementioned fundamental constituents, nu- 

 tritive materials including yolk granules or glo- 

 bules (deutoplasm) ; vacuoles, foreign enclosures, e.g., bacteria, etc., and 

 pigment (metaplasm) ; plastids (in plant cells) ; 

 chromidia (Fig. 7), masses of chromatic gran- 

 ules, presumably of nuclear origin, and probably 

 the raw material for certain differentiation prod- 

 ucts; and mitochondria or plastosomes. 



Mitochondria. Mitochondria are cytoplas- 

 mic elements of very variable form and of almost 

 universal distribution. These are destined to 

 bulk very large in immediate cytological investi- 

 gations. They may prove to be very important 

 elements of the more fundamental protoplasmic 

 structure and function. In the germ cells of 

 vertebrates, as in undifferentiated cells generally, 

 they are for the most part, granular (chondrio- 

 somes) (Fig. 8) ; in the somatic differentiated 

 cells filamentous or rod-shaped (chondriomites; 

 chondrioconts; pseudochromosomes) (Figs. 9 

 and 10). Both chromidia and trophospongium 

 (a canalicular network of the cytoplasm, prob- 

 ably concerned with circulation of nutritive material or secretion prod- 

 ucts) (Fig. 11) have been identified with mitochondria. Trophospon- 





FIG. 8. SPERMATID OF 

 OPOSSUM IN EARLY 

 STAGE OF METAMOR- 

 PHOSIS INTO A SPER- 

 MIUM. 



Showing granular 

 mitochondria, m, in the 

 cytoplasm, n, nucleus, 

 s, archoplasmic sphere. 

 X 2000. 



