CILIATED PITS OF PRORPIYNCHUS STAGNALIS. 



MARGARET R. HAASE, 

 UNIVERSITY OF VIRGINIA. 



The specimens used in this study were collected in the early 

 months of the year in a very small, slowly running stream, the 

 outlet of a spring, which is located about a mile west of the 

 University of Virginia. They occurred in greatest abundance 

 from twenty-five to forty feet below the spring, in the soft, 

 oozy, decaying organic matter at the bottom of the stream. 

 Prorhynchus applanatus was always found in equal, if not greater 

 numbers, along with Prorhynchus stagnalis. 



Some of the grass, weeds, and algae growing in the stream were 

 also taken along with the sediment, and the whole collection 

 placed in a large aquarium dish and left to stand for from twelve 

 to twenty-four hours. The rhabdocceles appeared at the edge 

 of the aquarium, near the water's surface, sometimes just beneath 

 the surface film. When a film of bacteria developed at the 

 surface of the water, the animals soon died, seldom being obtained 

 five days after the collection had been in the laboratory. By 

 keeping some of them in small dishes in spring water with some 

 small amount of the decaying matter collected in the stream, 

 and by adding fresh water every three or' four days, specimens 

 were kept alive for a maximum period of two weeks. 



The body of Prorhynchus stagnalis, when moving through the 

 water, is very slender or thread-like, being about the same width 

 all along the body-length. When at rest, the posterior half is 

 slightly broader, the average length of the body being about 6 mm. 



The anterior region of Prorhynchus stagnalis is the exploratory 

 region of the body. For, in response to a disturbance, the 

 region of the body, anterior to the ciliated pits, of an animal that 

 is quiet or of one that is creeping, is laterally expanded (Fig. I, 

 I.e.] and swayed to and fro ; while in addition to this the cilia of 

 the pits, during disturbance, are set into active motion. The 

 cilia of the ciliated pits are quiet when the animal is not excited 

 01 disturbed. 



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