2/O JOHANNA M. DIECKMANN. 



The next striking changes in the cloaca are the final modifica- 

 tion of the dorsal elevation to its adult form (cephalic portion 

 fused, caudal portion divided), and the development of the 

 diverticulum. The dorsal elevation, when last considered (n.o 

 cm.) consisted of two fairly well developed folds with the median 

 dorsal slit between them. At the cephalic end of the slit, cephalic 

 to the spermathecal opening, the slit was replaced by the slender 

 median dorsal fold which has been a feature of the cloaca since 

 early larval stages. In the 11.2 cm. animal the cellular condition 

 of this slender fold, and its increase in breadth, seem to indicate 

 hypertrophy. Gradually its caudal portion fuses with the two 

 folds caudal to it; its cephalic portion remains slender, however. 

 This fusion has been nearly completed at 13.3 cm., and fully at 

 13.5 cm. The hypertrophy is part of a general gradual over- 

 growth of the dorsal wall, which will be discussed further. By 

 the process just described, the dorsal elevation of the adult is 

 formed. It will be recalled that in the adult the elevation is 

 divided in its caudal portion, but cephalic to the spermathecal 

 opening, is fused; while still more cephalic the fused portion 

 gives way to three folds, the median slender one, flanked by two 

 smaller lateral ones. 



The diverticulum is absent in all animals smaller than 11.2 

 cm.; it, likewise, is formed by the overgrowth of the dorsal 

 wall previously mentioned. The diverticulum continues to 

 increase in size as long as the animal grows, for in the largest 

 animals its two prongs reach forward and partially flank the 

 spermatheca. 



DISCUSSION. 



The most interesting phenomenon in the cloaca of young 

 Gyrinophilus females is the development of the spermatheca. 

 The cellular area lying between the single mid-dorsal fold 

 cephalicly and the dorsal glands caudally, has been interpreted 

 in this study as its anlage. Even at this stage the mode of 

 formation of its tubules is indicated by the arrangement of its 

 cells perpendicular to the surface, and by a small bulb-like mass 

 of cells apparently about to grow out into the overlying mesen- 

 chymal tissue. This invasion is very clearly shown in the next 



