STUDIES ON THE CILIATES FROM SEA URCHINS

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Abstract
1. Entodiscus borealis (Hentschel), a ciliate infesting the alimentary tract of Strongylocentrotus dröbachiensis, when studied intensively, reveals a number of interesting manners of behavior as well as a series of complicated structures in connection with the cytostome and the fibrillar system. 2. The buccal cavity, guarded by a pair of membranous lips, has hanging from its roof a group of very long cilia. Embedded in the margin along its right wall is found a supporting rod for which the name stomatostyle is proposed. 3. Coördinating this stomatostyle as well as other parts of the body are two intricate sets of fibers arranged about two interconnecting centers: the anterior fibrillar center, and the posterior fibrillar center. These fibrillar structures, along with the transverse commissural fibers, found just beneath the pellicle, are interpreted as a well-developed neuromotor system. 4. After fixation with F. W. A. numerous vesicles. with outlets through the pellicle, are demonstrated in the anterior region. In considering the contents of the food vacuoles, these secretory vesicles suggest themselves as possible agents in producing cytolytic enzymes through whose aid the ciliate is able to attack and ingest portions of the intestinal mucosa of its host. In various regions about the cytostome and the pharynx there are found groups of secretory (?) granules. 5. E. borealis will exist for as long as 3 weeks in hanging drop cultures in sea water. Reproductive activity seems to occur only in the body of its host. The infestation appears to be maintained through early oral infection of young sea urchins.

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