No. r.] SPHYRANURA OSLERT. 45 



ovarian tract of the oviduct, the uterine tract is considerably- 

 folded, and undergoes a marked constriction before it passes 

 into the uterus. This organ is imbedded in a mass of unicellu- 

 lar shell-glands, a great many of which empty their contents into 

 the oviduct at the above-mentioned constriction, while others 

 pierce the dorsal and ventral wall of the uterus, towards which 

 their slender ducts converge. (Fig. 16, sgc.^ The shell- 

 gland cells extend out over the intestinal branches, and conse- 

 quently their narrow ducts, converging toward the uterus, pro- 

 duce a characteristic coarse striping over that organ, especially 

 if they are loaded with the shell-material, which is likely to be 

 the case if a mature egg has just been discharged and the 

 glands are about to furnish the shell for the next egg. On the 

 other hand, the ducts of the cells are not conspicuous unless 

 they are filled with the yellow granules of shell-stuff, and gener- 

 ally a good deal of difference may be traced in the cells them- 

 selves according to the state of their functional activity. 



We have frequently observed formless masses of shell-material 

 within the uterus, perhaps ovum or egg as centre, which has not 

 been enveloped in food-yolk balls. How the shell is moulded 

 upon the surface of the latter we are unable to say. It is pos- 

 sible that the epithelium of the uterus plays an active part in 

 this process. In the empty uterus these lining-cells are tall 

 (60 ^), and have a markedly reticular cytoplasm, the threads of 

 which are chiefly disposed in the long axis of the cell (Fig. 16), 

 toward the free end cf which is to be seen a nucleus of 12 ^ in 

 diameter ; when, on the other hand, the uterus is dilated with an 

 egg the epithelial cells are flattened into a very different form. 



The uterus never contains more than a single ^%^, resembling 

 in this respect that phase of Polystomuin integerrirnum which 

 occurs within the gill-chamber of the tadpole, but unlike the 

 ordinary form from the urinary bladder of the frog. 



It will be remembered that Polystomum oblongmn and ocella- 

 tum differ from P. integerrirnum as to the development of the &%%, 

 which takes place entirely outside the body in the latter, but gives 

 rise to a Gyrodactylus-like larva within the uterus in the former. 

 We have not observed development advance so far in Sphyra- 

 nura but we have reason to believe that this genus stands 

 midway between the above-mentioned forms in regard to the 

 extent of embryonic development within the uterus. We pro- 



