384 H. s. PKATT, 



same. There can be no doubt that the appendicular vesicle of young 

 appendiculate Distomes has the position, structure, and function of an 

 excretory vesicle (see Fig. 2), and I have no doubt that if one of 

 these worms were to be described by some one who was unacquainted 

 with the later and older forms, this vesicle would be called the ex- 

 cretory vesicle as a matter of course, and its only peculiarity would 

 be stated to be its unusually thick walls. 



I would thus interpret the appendix, provisionally, as the ex- 

 cretory vesicle or at least the hinder portion of it, which has evagin- 

 ated in order to increase the length of the body, perhaps for the ac- 

 commodation of a larger uterus. Whether this interpretation be cor- 

 rect only the embryology of the animal can determine. 



Methods. 



The preliminary studies on the worm described in this paper were 

 made at the Biological Laboratory of The Brooklyn Institute of 

 Arts and Sciences located at Cold Spring Harbor of which 

 Prof. Herbert W. Conn was the Director. Following the suggestions 

 of Looss (1894) the first studies were made on the live animal much 

 compressed. The worm is so minute that the pressure of the cover- 

 glass was sufficient for the purpose. It was found that if fresh sea- 

 water were occasionally introduced beneath the cover-glass, the animal 

 would often remain alive for many hours and become constantly more 

 transparent. In this way it was studied almost daily for several weeks 

 and the entire anatomy accurately made out. 



Large quantities of tow were preserved with acetic- corrosive- 

 sublimate, picro - sulphuric acid, and formalin, and the study of the 

 worm was continued at Haver ford College. A number of indi- 

 viduals, including those contained in the Copepod, those taken in the 

 act of making their way out into the sea-water, and those taken free- 

 swimming, were stained in Czokor's alum - cochineal and mounted 

 whole. Cross - sections and longitudinal sections were made of other 

 worms and stained with a variety of stains. The most useful stains 

 were Ehrlich's or Delafield's haematoxylin either followed by eosin 

 or not. Iron haematoxylin, satïranin, and the Biondi - Heidenhain 

 three-color-stain were also used and found of use in differentiating the 

 organs. 



