229] TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY 35 



completely enough to be noticeable externally, as a consequence almost all the 

 specimens appeared to be formed of only two parts. The reason for this is 

 the precocious or rapid development of the organs in the first budding zone, so 

 that the separation takes place before the organs of the next zone have become 

 visible from the exterior. Sections of such a zooid chain show the relative 

 development of the several parts The situation is briefly this: The brain 

 ganghon on the dorsal side and the buccal indentation on the ventral side of the 

 digestive tract become about half-formed before the integument and paren- 

 chyma begin to narrow in at all. By the time this pushing-off process is nearly 

 complete, the mouth has broken thru, the sensory pits are formed, and the 

 last connection is by means of the intestinal cavity w^hich is continuous thru 

 the proboscis-like anterior end of the posterior zooid. In this species, such a 

 connection remains intact for a longer time than in most others and it is broken 

 off only just before the two individuals separate. Generally, in both individuals 

 of such development, a histological examination v/ill show the beginnings of 

 another fission zone in the start of a new pharynx and another brain ganglion. 

 The fission plane here is quite exact and sharply cuts the parts, while in some 

 forms the constriction is gradual so that the adjacent parts do not he very 

 close together. 



Comparing this species with others of the genus, it seems very blunt and 

 solid by the side of the more slender, agile types. The proportion of diameter 

 to length is very much greater than is common. 



Since writing the above I have had the opportunity to see this species 

 living in one of the ponds at Fairport. During the early part of July the num- 

 bers were so great that a canton flannel cloth was used to strain them out from 

 the water running into some of the smaller tanks. Their presence caused much 

 anxiety because it seemed probable that the food was at least in part made up 

 of glochidia. The individual rhabdocoels were v/hite and opaque, conspicuous 

 and up to 3mm. in length, larger than other specimens of the same species. 

 They exhibited the characteristic stifif cylindrical form and the usual two 

 zooids. One strange fact, not yet explained, was their almost complete dis- 

 appearance by the first of August. 



Stenostoma glandiferum nov. spec. 

 Figure 47 



This form was present in several ponds in which the bottom was muddy 

 and covered with a fine layer of silt. The plant and animal species varied, but 

 in all cases the environmental conditions were much the same. Except in 

 one pond, the sim and wind had much efifect upon the temperature and quiet- 

 ness of the water. Stenostoma leucops was also present with some degree of 

 frequency. There was always either some filamentous alga or Chara, and the 

 living surroundings were ideal for all types of microscopic animals. Most of 

 the food material seems to be taken from the silt and very httle from other 



