CELL CONSTANCY IN THE GENUS EORHYNCHUS 277 



10. The female genital apparatus 



Eorhynchus gracilisentis. The vagina presents a clear example 

 of constancy of number and arrangement of the nuclei. Four 

 large nuclei (figs. 11, 12 and 13, v) are found in its inner muscular 

 layer between the genital orifice and the sphincter vaginae. Two 

 nuclei are associated with the sphincter. The outer non-muscular 

 layer of the vagina in the region of the sphincter contains three 

 nuclei. Cephalad from the sphincter the vagina has a short 

 rounded region consisting of a thick walled tube through which 

 the embryos must pass from the uterus into the orifice of the 

 sphincter. This heavy walled portion of the vagina bears four 

 large nuclei. Anteriorly, the outer wall of the vagina passes 

 over into the single-walled uterus with its large sac-like cavity. 

 On the dorsal side of the uterus at its junction with the vagina 

 there is an enlargement of the wall in which are found two nuclei, 

 the only ones associated with the uterus. Figures 11, 12 and 13, u, 

 V, and vs, show the relations of these parts, together with a repre- 

 sentation of the nuclei. The selective apparatus (fig. 11, so), 

 because of its extremely complicated structure, gives consider- 

 able trouble when an attempt is made to compare the nuclei of 

 one individual with those of another. The eight nuclei shown in 

 the drawing just cited have been found in every individual studied, 

 but several other nuclei which occurred in this region in some in- 

 dividuals could not be found in others of the same species. The 

 hard shelled embryos with which the body of a mature female is 

 filled hide this structure almost completely in toto mounts, and in 

 serial sections the embryos frequently cause it to be so torn that 

 very little of the actual relations may be made out! Extending 

 posteriad from the dorsal wall of this selective apparatus are two 

 muscular strips whose function is evidently to support these 

 organs since each finds a point of attachment on the dorsal wall 

 of the body. One nucleus occurs in each of these (fig. 11, ssa). 

 On either side of the genital orifice of the female there extends 

 a broad fan shaped ligament which becomes attached to the 

 dorsal wall of the body cavity (fig. 15, fl). In the broad portion 



