180 



At present little can be positively stated concerning the importance 

 of the penial bulb in separating the species of a genus owing to the 

 incompleteness of the data for the whole group. The writer has found 

 that in each species studied the structure of the bulb is constant, and 

 that in no case is it exactly duplicated in the bulb of another species. 

 In certain genera, as, for example, Mcscnchyfrcriis and Enchyfrarus, 

 where the penial structure is usually very complicated and the \aria- 

 tion rather wide, it is not difficult to find in the structure of the penial 

 apparatus distinguishing characters for species. The main difficulty 

 appears in the lumbricillid bulb, particularly in Fridcricia in which 

 the structure of this organ is at its simplest, and in which the varia- 

 tion among the species is so small that although the structure of the 

 bulb is uniform for each species, it is difficult to get a distinct diag- 

 nostic character. 



Observations and Experiments on 

 lumbricieeus rutieus n. sp. 



The writer's attention was called to this species in April, 1911, 

 when alcoholic material of the same was turned over to him by Dr. 

 S. A. Forbes, to whom it had been sent by the Director of the Thirty- 

 ninth Street Sewage Testing Station, Chicago, Illinois. The material 

 was accompanied by the information that this worm occurred in great 

 abundance in the sprinkling filter beds. The specimens were in such 

 poor histological condition that an attempt to determine the species 

 was abandoned. Later, June 22, 191 1, Mr. A. A. Girault collected 

 similar material at Chicago, made a brief record of the general condi- 

 tions of the habitat, and had a large number of the specimens properly 

 killed and fixed. This material formed the basis for the morphological 

 and systematic work on this species which has already been included 

 in the paper (pp. 143-151). During October, 1912, the writer spent 

 three weeks at this Testing Station, making certain investigations on 

 this species, and the major part of the data on the living material 

 which follows were accumulated during that period. 



HABITAT 



Since this is the first published record of an American species of 

 Luuihricillus which occurs in connection with sewage, and since its 

 great abundance indicated a particularly favorable environment, the 

 habitat was carefully studied and will be described at some length. 

 Much of the detail which follows is essential to subsequent discus- 

 sions and explanations of results. It may be noted here that there 

 are records of about six European species which occur normally in 



