42 ILLINOIS BIOLOGICAL MONOGRAPHS [162 



not occur simultaneously in all of the germ cells but progresses from the 

 buds toward the dorsal part of the ovary. The full-grown oocyte is about 

 0.023 mm. in diameter and is surrounded by a definite membrane. At the 

 center of the cell is found a large nucleus, while the cytoplasm is filled with 

 yolk granules. The nucleus has a diameter of about 0.006 mm. and consists 

 of a large, central chromophil mass surrounded consecutively by an achro- 

 matic and a chromatic layer (Fig. 106). 



Toward the anterior end the ovaries gradually decrease in size, the space 

 surrounding them, even on the dorsal side, becoming filled with parenchyma. 

 In some cases the invading parenchyma interrupts the ovaries at places, 

 forming bead-like masses following each other in longitudinal series. The 

 formation of these masses is even less regular than the location of the buds 

 on the ventral sides of the ovaries. 



At the posterior end the oviducts are formed by continuations of the 

 ovaries and they unite to form the cloacal gland and the seminal receptacle 

 (Figs. 109-11). It has been impossible in the very early stages to 

 recognize the germ cells in this region, but at the time the ovaries are 

 still round they pass without interruption back to the point of union 

 and form a mass of cells, the rudiment of the cloacal gland, around 

 the ventral side of the intestine. At that stage the lateral diverticula 

 connect with these cells near the latero-posterior margins of the mass 

 while the ventral diverticulum joins them somewhat anterior to those 

 points. The seminal receptacle exists as an anterior lobe of the cell mass. 

 The membrane surrounding those structures is continuous with those sur- 

 rounding the ovaries and no difference is apparent in the character of the 

 cells of the cloacal structures and the ovaries, either in staining reaction 

 or in structure. 



Later the cells become modified so that it is impossible to distinguish 

 between those that have been derived from the intestine and those derived 

 from the germ glands. The oviducts become indistinguishable behind the 

 points where they enter the cloacal gland. Anterior to those points the 

 cells in the oviducts rearrange themselves so as to form definite walls 

 around the central ducts (Figs. 88-90, 93-95). Even at that stage the 

 change from oviducts to ovaries is a gradual one, the oviducal walls 

 continuing farther anteriad on the ventral side than on the dorsal. 



The cloacal gland takes up a median position beginning somewhat 

 posterior to the points at which the ovaries were previously inserted into 

 the intestine and extending anteriad to the seminal receptacle, into which it 

 opens broadly (Figs. 78, 93-95, 99, 100). The intestine opens into the dorsal 

 side of the gland near its posterior end, the oviducts open into the latero- 

 ventral sides near the anterior end. The cells of the gland become closely 

 packed and form finger-like projections that extend inward and forward 



