1892.] AaUATIC OLIGOCH^TOUS WORMS. 353 



The worm consisted of eight segments, after which came a bud 

 that had been in part detached ; but I succeeded in finding the rest 

 of it upon the slide ; the number of segments, therefore, is approxi- 

 mately the same as Leydig gives for ^olosoma niveum, and the 

 same number also that Vejdovsky gives for JEolosoma variegatum. 

 The prostomium, however, was large, squarish in front, and dis- 

 tinctly wider than the rest of the body. Leydig figures a very 

 inconspicuous prostomium, which, in front at least, is actually nar- 

 rower than the succeeding segments. With regard to the colourless 

 oil-drops in the integument, I could see no structures that were at 

 all obvious. There was no appearance such as is represented in 

 Leydig's figures. Nor were there any clearly defined droplets such 

 as Vejdovsky figures in his Molosoma variegatum. I should be 

 inclined to say that there were no oil-drops present at all. The 

 epidermis was much more like that of a Naid or a Chcetogaster than 

 an ^olosoma ; and even when the worm was treated with potash, 

 which produces such recognizable effects' upon the oil-globules of 

 other species, no alterations were observable, except that the worm 

 was stained a faint yellowish. And yet there is no doubt whatever 

 that I am right in referring the Annelid to the genus JEolosoma. 

 In all other particulars it agreed with that genus. The prostomium 

 was ciliated on the under surface, and the lateral ciliated pits are 

 present. The mouth appeared to be situated rather further back 

 than it has been usually figured for this genus ; the constriction 

 which marks off the prostomium posteriorly was situated some little 

 way in front of the actual mouth-opening. 



The most important difference, however, from Leydig's description 

 concerns the setae. In all the species oi Molosoma at present known, 

 with the exception of Vejdovsky's ^olosoma tenebrarum and (if it 

 be really distinct from this) J^oloso7na leidyi^, there are only 

 capillary setae present in both dorsal and ventral bundles. In the 

 two species above mentioned cleft sigmoid setse are also to be found ^ 

 In the specimen of ^olosoma niveum described here I have also 

 found these sigmoid setsfc, and it is principally the fact of the occur- 

 rence of these setse which leads me to doubt the identity of this 

 worm with Leydig's ^olosoma niveum. Had they been present 

 Leydig would hardly have overlooked them. The existence of these 

 sigmoid setae also, I may j)oint out, precludes the possibility of this 

 worm being the young of JSolosoma quaiernarium, and I do not 

 think that it has anything to do with yEolosoma tenebrarum. 



In the first seta- bearing segment there were not any sigmoid 

 setae, but four capilliform setae in each of the dorsal, and three in 



' " Note upon the Green Cells in the Integument of JEolosoma tenehrarum" 

 P. Z. S. 1889, p. 51. 



" Notes upon certain Sjjecies of Molosoma"Aj\n. Mag. Nat. Hist., Oct. 1889. 



^ F. W. Cragin, " First Coutribution to the Invertebrate Fauna of Kansas," 

 Bull. Wasbb. Coll. Lab. 1887, no. 8, p. 81. 



3 I am not quite certain that the species described by me as Molosoma tetie- 

 hrarum (P. Z. S. 1889, p. 51) is re.illy identical with Vejdovsky's species; I 

 could not detect the cleft at the end of the setis, and the colour of the oil-drops 

 appears to be rather different. 



