80 XICHOLS— SPERMATOGENESIS OXISCUS ASELLUS LINN. [April 4, 



matids in a stage of development later than that of follicle {a). 

 Along the margin of the follicle are found scattered small groups of 

 spermatagonia (Fig. 2, spg). The third and most anterior follicle 

 {c) contains chiefly spermatocytes in a late prophase. Groups of 

 spermatogonia similiar to those of follicle (^b) are here also found 

 scattered along the margin and nearly filling the extreme apical 

 portion. The follicle cells in the basal region are undergoing not 

 only active amitotic division, but to a certain extent degeneration 

 (Fig. 5). Their active multiplication or fragmentation causes them 

 to crowd in toward the axis of the follicle. 



From a comparison of the extent of these growth regions in the 

 three follicles, the developmental cycle may be conceived somew^hat 

 as follows. The spermatozoa, when fully formed, are forced into 

 the vas deferens. Since they have no motion of their own, this is 

 probably caused by the contraction of the muscle layer of the folli- 

 cle, perhaps assisted by the pressure of the growing cells in the 

 apical region. During this process, the spermatogonia in the apical 

 portion of the follicle divide and come to fill the space left vacant 

 by the discharged sperm. The rate at which this replacement takes 

 place and the comparative development of the cells in the two 

 regions may vary in different follicles, for I have preparations in 

 which few or no spermatozoa are seen — in other words, most of them 

 had probably been discharged, and at the same time the replacing 

 spermatogonia are scattered and itw in number. In others, as is 

 shown in the diagram (Fig. 2a), the spermatozoa, in an early stage 

 of development, occupy the basal portion of the follicle, while the 

 apical portion is packed with spermatogonia. The majority of the 

 spermatogonia thus filling up the follicle proceed in their develop- 

 ment, while the remainder form the groups of cells along the margin 

 of the follicle already described in follicles {b) and (^), and which 

 are destined later to again supply a new generation of cells. The 

 spermatids also proceed in development and are forced into the vas 

 deferens. A condition like that represented in diagram {b) (Fig. 2) 

 thus arises — the basal region filled with spermatozoa in a late stage 

 about to pass into the vas deferens and the apical region with, cells 

 which have progressed as far as the synapsis stage. Later, the 

 spermatozoa having been completely discharged, the cells of the 

 apical region come to occupy the basal part of the follicle, being 

 now less compactly pressed together (Fig. 2c). Their development 

 progresses until, having become mature spermatozoa, they pass into 



