Near 2:i] THE MORPHOLOGY OF DERO VAGA. 145 
turbed this whole apparatus is protruded from the case and is 
turned with the concave side of the disc uppermost. When 
the apparatus is contracted the disc is so folded as to give the 
appearance of four lobes, which, with the two well-defined 
ventral lobes, make up the half-dozen blunt papillae described 
by Leidy. 
The case (Fig. 1) consists of a thin hyaline tube covered 
over with dead Lemna leaves, statoblasts of fresh-water Bryozoa, 
Arcella shells, or small pieces of almost any substance which 
may be floating on the surface of the water in which they live. 
As the worm grows longer the case is also increased in length, 
and when fission is complete the worms place their heads 
together at the middle of the case and break it in two. Each 
worm goes away with one half of the old case. The cases of 
worms found on the surface of the water will float when the 
worm is driven out, while those found on the bottom will sink 
under similar conditions. Worms have been observed to change 
their position gradually from surface to bottom and from bottom 
to surface, according to the location of the food supply. 
Locomotion is effected in a jerking manner by extending the 
body some distance out of the case and attaching the anterior 
portion by means of the pharynx and the ventral setae and 
then contracting the body, pulling the case forward. At the 
time of the development of the sexual organs the worms have 
been observed to leave their cases and crawl about on the 
bottom of the dish. 
The food taken is apparently entirely vegetable matter and 
consists of desmids, algae, and at times the fronds of Lemna 
and Wolffia. 
Sexual organs are developed during the first two weeks in 
July. However, worms kept over winter in an aquarium 
showed sexual organs as early as April 1. A clitellum is 
formed which covers segments V—VII. Spermathecae occur 
in segment V and the atrium of the sperm duct is plainly visi- 
ble in segment VI. Egg masses fill a large part of the body 
cavity posterior to the clitellum. Eggs outside of the body 
have not been found and the manner of laying the eggs is 
unknown to me. 
