1892.] AQUATIC OLIGOCHiETOUS 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 sHde ; the number of segments, theret'ore, is approxi- 

 matel}' the same as Leydig gives for j^olosoma niveum, and the 

 same number also that Vejdovsky gives for ^olosoma variegatum. 

 The prostomium, liowever, 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 ^olosoma 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 Chcstogaster than 

 an ^olosoma ; and even when the worm was treated vpith 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 ^olosonia. 

 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 setse. In all the species oi ^olosoma at present known, 

 with the exception of Vejdovsky's JEolosoma teyiebrarum and (if it 

 be really distinct from this) JEolosoma leidyi ^ there are only 

 capillary setse 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 JEolosoma niveum described here I have also 

 found these sigmoid set8&, 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 ha\e overlooked them. The existence of these 

 sigmoid setae also, I may point out, precludes the possibihty of this 

 worm being the young of ^Eolosoma quaternarium, and I do not 

 think that it has anything to do with JSolosoma tenebrarum. 



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

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



1 " Note upon the Green Cells in the Integument of Molosorm tenebrarum," 

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



" Notes upon certain Species of JSolosoma,"Ann. Mag. Nat. Hist., Oct. 1889. 



- F. W. Cragin, " First Contribution to the Invertebrate Fauna of Kansas," 

 Bull. Washb. Coll. Lab. 1887, no. 8, p. 31. 



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

 brarum (P. Z. S. 1889, p. 51) is really identical with Vejdovsliy's species; I 

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

 appears to be rather different. 



