No. 3.] ORGANS IN PHASCOLOSOMA GOULDII. 389 



a condition in which the radial zone is enlarged, and extends 

 down into the protoplasm of the cell, while the sack within 

 remains small and surrounded by an extensive zone of delicate 

 threads. At what appears to be a very late phase the walls of 

 some of the sacks are seen to be broken down, the sacks are 

 confluent, and in all probability entire cells disintegrate. 



After a comparative study of a large number of these organs 

 representing many conditions, the following explanations of the 

 different appearances seemed justified. The transparent zone 

 traversed by radial fibers as shown in PL XXXV, Fig, 16, enlarges 

 and occupies more of the cell. The sacks within enlarge in turn, 

 and finally, as the periphery of the cell is approached, the sack 

 comes to occupy the whole space. The enlargement of the sack 

 within the radial zone is the result of the secretory activity of 

 the cell — the sack being filled with a clear secretion which is 

 conducted to the outside by means of the common duct aris- 

 ing from the union of the several smaller canals. The delicate 

 radiating threads surrounding the sack probably represent the 

 protoplasmic reticulum filling the cell, the threads of the 

 reticulum in the vicinity of the sack being perhaps stretched 

 by the accumulation of the secreted material in this region and 

 thus caused to assume the radiating character shown. That 

 the space between the sack and the wall of the vacuole, as 

 figured in PI. XXXV, Figs. 15, 16, and 19, is not an artifact 

 due to the action of reagents, is proved, I think, by the exami- 

 nation of fresh tissue under the microscope, in which case the 

 sack appears as a highly refractive body, surrounded by a sec- 

 ond clear zone which evidently represents the region traversed 

 by the delicate radiating threads. 



Comparison with other accounts of the epidermal organs of 

 GepJiyreans. — Of the various accounts which have been given 

 of the epidermal organs of the Gephyreans, the only ones which 

 will be considered here are those of Andrews ('90), Ward ('91), 

 and Jourdan ('91), these being the only papers, so far as I know, 

 which offer observations upon the epidermal organs, interesting 

 for comparison with the results here presented. 



Andrews, who deals with the same worm as the one treated 

 in the present paper, divides the epidermal organs into three 



