186 



Wm. S. Marshall, 



itH median part. A fevv of the nuclei are nearly spherical, tliese 

 are more apt to be found in the center of the tubule than near its 

 wall. Here and there are groups of cells similar to those described 

 for Our earlier stage. 



Where the distal passes into the middle region of the tubule, 

 the change is quite abrupt, the small, ovoid nuclei giving place to 

 the larger, spherical ones; the cells also change from an elongated 

 to a more rounded form, At this transition region the tubule becomes 

 somewhat wider. But few mitotic figures were present in this stage, 

 not more than four or fiye being found in any tubule of the ovary. 



Ovary C. This is the youngest ovary we found in larvae after 

 they had ceased feeding, and enclosed themselves in the cell of their 

 nest. The larva was of course füll grown, the tubules were each 

 1.44 mm in length. Distally, each tubule is long and narrow^ and 

 not straight throughout its entire length but terminally, it is beut. 

 In this latter region, and for some little distance down the tubule, 

 many of the cells extend entirely across it; sometimes they are 

 equally broad throughout their entire length, but oftener pointed at 

 one end (Fig. 14). The nuclei of all the cells in this part were very 

 similar, any slight differences they showed being in the arrangement 

 of their contents. Each nucleus has two, seldom more or less, 

 nucleoli, quite large and irregulär in shape and position; each one 

 is surrounded by a thin layer of achromatin from which Strands pass 

 to the nuclear membrane. In these achromatin Strand lies a number 

 of chromatin granules, these do not stain evenly some being darker 

 than others. The cytoplasm of these cells is quite irregulär in 

 appearance and distribution. Passing further down the tubule we 

 find it widening and the cells becoming arranged in a fairly even 

 layer along its wall. Next we notice that a few cells appear in the 

 central part of the tubule — not in a lumen because none is present — 

 so that, here and there, one can find three cells, instead of two, 

 across the tubule. The nuclei remain unchanged, but a few of the 

 centrally situated cells become more rounded. As we pass down 

 the tubule these central cells become more and more abundant, and 

 finally, in the median portion of the tubules (Fig. 13 ov)^ the long 

 narrow cells have almost entirely disappeared. 



At the distal end of this median portion, difterentiation takes 

 place more rapidly than at any other part i. e. the change of the 

 nuclei from an oval to a round form, and the enlargement, and 



