Species of North American Oligochcsta. 293 



are sometimes found in the algiB, sometimes in the mud 

 at the bottom of the lake, and sometimes on the shore 

 above the level of the water, under rubbish which is kept 

 moist by the springs constantly flowing from the bank. 

 Among specimens collected last February from a situa- 

 tion like that last described, one individual was found 

 that was sexually active, with others that had been in 

 that condition recently enough to be of use in gaining 

 a knowledge of the sexual organs. 



The worms are 30-60 mm. in length and .6-.8 mm. in 

 diameter. The number of somites is usually 150-200, 

 and sometimes even greater. The setse are in four rows 

 of bundles with two setae in each. They are .15-2 mm. 

 in length, with bifid extremities, and have the same 

 form as those of Lumbricuhis variegatiis Grube as figured 

 by Vejdovsky (18, Taf. XII, Fig. 27). The length of 

 the prostomium in alcoholic specimens is about equal 

 to that of the first three somites taken together, and 

 its width is almost as great as the diameter of the first 

 somite. The width is nearly uniform for the greater 

 part of the length, and the extremity is bluntly rounded. 

 The brain is quite similar to that of L. variegatus Grube 

 as figured by Ratzel (11, PL XLIL, Fig. 10), if I under- 

 stand his figure, but not if Beddard's interpretation (1, 

 p. 212). be correct. A comparison of Ratzel's figure 10 

 with figures 12 and 13 of the same plate makes it quite 

 evident that the supracesophageal ganglia are repre- 

 sented by Ratzel in a position the reverse of the nor- 

 mal one, so that what is described by Beddard as the 

 anterior [)ai-t is i-eally the i)osterior part, and vice versa. 

 In the brain of Thinodrilus incondans the masses of cells 

 are upon the posterior part, and are not united hy a 

 narrow layer of cells as represented in Lumbri cuius vari- 

 egatus, although such a layer is present upon the outer 

 surface of the brain, and if no sections were made might 

 be supposed to connect the two masses. The median 

 part of the brain, which connects the two lateral 



