266 JOHANNA M. DIECKMANN. 



DEVELOPMENT OF THE SPERMATHECA AND CLOACA. 



The cloaca in larvae ranging in size from 7.7 to 10.0 cm. is 

 very simple; there are few folds in its lateral wall and these 

 disappear on distention of the cloaca. One, however, in the 

 dorsal wall, persists in spite of distention. It is located just 

 caudal to the dorso-ventral expansion into which open ureters, 

 oviducts, gut and bladder. Because of its location, its slender- 

 ness, and its delicate epithelium, this fold is interpreted as the 

 medial of the three folds into which the dorsal elevation divides 

 in the adult (Figs. 14, 8, and 9). Caudal to this in the roof 

 of the cloaca, the epithelium grows very much thicker and has a 

 well-defined row of basal cells and basement membrane (Fig. 15). 



In two larvae of 10.3 and 10.5 cm. respectively, a noteworthy 

 change is observable. Over a short area caudal to the slender 

 fold described above, and dorsal to the vent, the basal row of 

 nuclei is not distinct, and the nuclei of the epithelium are small 

 and numerous. The overlying tissue is likewise richly cellular, 

 and is mesenchymal in character. Upon superficial examination 

 the nuclei of epithelium and overlying tissue are indistinguishable 

 and seem to intermingle. Even upon closer examination they 

 are quite similar, but a basement membrane, though very delicate, 

 is apparent. The epithelium of this area, which stands in clear 

 contrast to that of the rest of the cloaca, has been termed for 

 convenience, the "cellular area," and is regarded as the anlage 

 of the spermatheca (Fig. 16). The epithelial cells of the area 

 show a distinct tendency to arrange themselves in rows perpen- 

 dicular to the surface. Spaces often appear between the rows, 

 but might be interpreted as artefacts. In one place a small bulb 

 of cells has formed within the epithelium (Fig. i6a). Fig. ija 

 shows an early stage in the development of dorsal glands from 

 the same animal. It will be seen that the gland tubule is in a 

 slightly more advanced stage than the tiny bulb of cells in the 

 cellular area. Both gland and spermathecal tubules are epithelial 

 outgrowths. 



One would probably not be justified in interpreting the picture 

 seen in the cellular area, if taken alone, as an invasion of epithelial 

 cells into overlying tissue were it not for the unequivocal evidence 

 of such invasion discernible in the next stage. (The term 



