I02 HODGE. [Vol. VII. 



Reproductive Tissues. 



No description of the formation of spermatozoa is necessary. 

 Views as to details differ among different authorities (39, p. 900 ; 

 67, p. 688 ; 22, p. 17) ; but all are agreed as regards nearly 

 everything that touches our point of view. In general, the 

 nucleus is transformed into the head and the protoplasmic re- 

 ticulum develops into a vibratile flagellum. The head assumes 

 peculiar forms in different types, but whether it shows any 

 increase or decrease in size I am unable to say. Processes of 

 division have recently been observed, in which a portion of the 

 head is extruded after the fashion of polar bodies (5). 



The ovum also presents features of interest. Here both 

 nucleus and protoplasm increase in size, often at the expense 

 of surrounding cells (18, pp. 5 ff.), the nucleus in maturation suf- 

 fering a reduction to one-fourth its chromatin by extrusion of 

 polar bodies (63). Besides changes in nucleus and food material 

 the reticulum often assumes a peculiar structure, to form the 

 "zona radiata" around the outside of the ovum. 



It may be well to bear in mind all phases of protoplasmic and 

 nuclear activity passing by the names of ookinesis, cytokinesis, 

 or karyokinesis. Let us see if anything in the functional ac- 

 tivity of other tissues may be found to resemble these processes, 

 or those of direct nuclear division. 



Gland. 



Of importance in their influence upon theories of secretion 

 were the first experiments of Heidenhain. Secretion could no 

 longer be thought of as the " straining off " of Malpighi (47, 

 I, p. 464), or the " diffusion stream " of Deutroschet, when the 

 activity of the cells themselves had once been demonstrated. 

 Heidenhain (19, 20, 21) found that, as the cells secreted, their 

 appearance changed in a marked degree. In general, a granular 

 zone next the lumen disappeared, leaving the cells shrunken. 

 The nucleus in the meantime, from being small and irregular in 

 outline, became swollen. Protoplasm grew again, and from its 

 substance arose a new zone of granules. Sooner or later the 

 secreting cells go to the ground and new cells spring up to take 

 their places. 



