CLOACA AND SPERMATHECA OF GYRINOPHILUS. 2J3 



of the whole dorsal wall of the cloaca, as indicated in Fig. 27 

 by the small arrow ahead of the spermatheca, and the curved 

 arrow behind it. This overgrowth would (i) elongate the 

 common tube and lift its caudal portion farther from the cloaca; 

 (2) form the dorsal elevation and cause the fusion of its two 

 limbs ahead of the spermatheca; (3) produce the diverticulum; 

 and (4) bring about the final change in direction of the tubules. 

 The two processes described above, elongation with shifting 

 of parts, and overgrowth of the dorsal wall, are not independent 

 but overlap in time. This is readily shown by the fact that the 

 folds \vhich form the caudal part of the dorsal elevation begin 

 to form at the "cellular area" stage, and are well developed 

 while the early spermatheca still lies over the vent. 



SUMMARY AND CONCLUSIONS. 



1. The cloaca of Gyrinophilus females is characterized by the 

 presence of a dorsal elevation which most closely resembles that 

 in Eurycea, and a diverticulum like that of the Plethodons. 



2. The spermatheca is of the complex type, with a branched 

 common tube, and numerous flask-shaped tubules. 



3. Suggestive though inconclusive observations on mating and 

 ovulation have been previously summarized (p. 264). 



4. Preceded by the appearance of a cellular area, suggesting 

 the invasion of epithelial cords into overlying tissue, the sperma- 

 theca begins to develop at the time of metamorphosis, as a 

 mass of tubules, aggregated about a small depression in the 

 dorsal cloacal wall which becomes the common tube. 



5. Coincident with a cephalic shift in position of the whole 

 organ, the tubules begin to change their direction to a pre- 

 dominantly caudal one, and the two folds forming the dorsal 

 elevation, develop. This is followed by a fusion of these two 

 folds cephalic to the common tube, elongation and change of 

 form of the latter, completion of the change of direction of the 

 tubules, and finally the development of the diverticulum. These 

 changes in the cloaca are interpreted as being caused by cephalad 

 growth of the dorsal wall at a more rapid rate than that of the 

 ventral wall, and an overgrowth of the whole dorsal wall. 



