402 lUinols State Laboratory of Natural History. 



one hundred specimens observed under normal condi- 

 tions, or after but brief captivity, fourteen had the first 

 budding zone at XV | XVI, sixty-nine at XVI | XVII, 

 sixteen at XVII j XVIII, and one at XVIII ] XIX. In 

 no instance have I found Bourne's z' to be other than 

 seven. I may state here that after numerous observa- 

 tions upon several species of naidiform worms 1 have 

 found tliat n is extremely variable in individuals of the 

 same species, and, also, in a less number of species, that 

 the number of somites in the sexually mature worm is 

 not constant for a species. 



Mesoporodrilus asymmetricus n. g. et n. sp. (PI. 

 XXXVI., and PI. XXXVII., Fig. 11 and 12.) 



The following description is based upon two specimens 

 of a lumbriculid species which were found in July of 

 the present year in the sand of the east shore of Quiver 

 Lake, near its foot, and in a situation where small 

 springs of water kept the sand wet and cold. The speci- 

 mens were received at a time when a study of the living 

 worms could not be made, and they were immediately 

 fixed and preserved. One of the specimens was not in a 

 very good condition, and was chiefly valuable in con- 

 firming the observations upon some of the more im- 

 portant characters of the other. 



The worms are without pigment, and quite delicate in 

 appearance. They are 30 mm. in length and .5 mm. in 

 diameter, the number of somites in one apparently com- 

 plete specimen being 65. They are provided with a 

 proboscis that in length equals the diameter of the first 

 somite. There are four pairs of pointed setae on each 

 somite (PL XXXVI., Fig. 9). The clitellum extends 

 from the middle of IX to the middle of XIII, and is 

 conspicuous. 



The pharynx extends through III and IV (PI. XXXVII., 

 Fio-. 11). The epithelium of the dorsal half of its wall 

 is thick and ciliated (Fig. 12), although thinner aloug 

 the median line of the fourth somite than elsewhere. 



