THE ANATOMY OF ONOHOLAIMUS VULGARIS, BAST. 131 



and a posterior, uniting to open by a single aperture to 

 the outside. Tiie tubes are straight, not bent back upon 

 themselves as in the adult, but, as will be explained farther 

 on, the fundus does not correspond with the commencement 

 of the first part of the ovarian region in the adult, but with 

 the fundus of the ovarium ceecum. 



The tubes are only potentially tubes ; towards the fundus, 

 where the oogonia occur, these cells completely fill the lumen; 

 in that part destined to become vagina the lumen is occupied 

 by a solid core of cuticle, and between these two regions the 

 " tubes " consist of solid rods of protoplasm, which show 

 their tubular nature only by the arrangement of the nuclei 

 in a single layer around the periphery. 



If each tube were divided into five parts, the first part, 

 counting from the fundus, would contain the oogonia (PI. 8, 

 fig. 25). Here the wall [gw] is of flattened epithelium, not 

 showing cell outlines, the nuclei flattened oval, with chromatin 

 granules and nucleolus. 



At the junction of the first and second fifths in the ventral 

 wall the germinal portion of the epithelium is situated. Here 

 the protoplasm of the wall grows into the lumen, the nuclei, 

 still retaining the same characters, become larger and more 

 spherical. The oogonia (og) as they develop from this proto- 

 plasmic projection pass, not towards the external aperture, but 

 towards the fundus. The youngest nuclei which can be 

 definitely recognised as oogonial resemble the nuclei of the 

 germinal projection, but are more oval, and are larger, 

 measuring 0"0016 mm. in diameter, and the chromatin granu- 

 les are smaller and fewer in number. A transverse section 

 at this point shows about eight such nuclei. The protoplasm 

 is scanty, shows no cell outlines, and stains with basic dyes. 



In the later stage of development the nuclei have become 

 still largei", 0*0161 mm., and consequently there are fewer in 

 a transverse section. The chromatin granules have disap- 

 peared, the nuclear vesicle being filled by a finely granular 

 material which does not stain, the nucleolus is large. The 

 protoplasm is relatively greater in amount. The immature 



