250 DISCOVERY REPORTS 



is broadly spindle-shaped, and there is neither a distinct duct nor any associated glands ; 

 in Benham's worms the ampulla and duct are distinct, the ampulla being (from the 

 figure) considerably wider, and there are two glands. Further, there is a small penial 

 body in M. werthi, none in Benham's specimens ; one prostate, apparently, in M. werthi, 

 but a number of glandular masses aggregated into a few groups in Benham's worms. 

 If the two worms described above (M. griseo and M. aestmim), with the same pigmenta- 

 tion, possess, like Benham's specimens, distinctive structural differences such as would 

 ordinarily be sufficient to characterize separate species, then I think Benham's reason 

 for merging his worms with Michaelsen's will disappear, and we shall have a group of 

 species, closely related, no doubt, with the peculiar pigmentation as a common feature. 



The worms which I have called M. grisea differ from M. zverthi principally in the 

 testes (massive, with clefts in their substance but not divided into free club-shaped 

 lobes) ; in a very distinct division of the spermathecal apparatus into bulbous duct and 

 spindle-shaped ampulla, and in the presence of two associated glands; in possessing 

 two large and definite prostates ; and in having copulatory glands, of only moderate size, 

 in segment xv (instead of very large glands, in xiv). 



The specimens from South Georgia, M. aestimm, are distinguished from M. werthi 

 principally by the extraordinarily large number of setae per bundle; the tubular 

 spermathecal apparatus with well-defined duct and associated glands ; the prostates, as 

 in M. grisea; the small or very small copulatory glands in xiii and xiv; and probably by 

 considerable differences in the penial body. M. aestuum is distinguished from M. grisea 

 by the number of setae per bundle, the form of the spermathecal apparatus, the small 

 and divided testes, the copulatory glands in xiii and xiv (instead of in xv only), and by the 

 absence of the ventral epithelial plate in x. 



The value of this last feature is not quite certain ; it is not described in M. werthi or 

 by Benham for his specimens, but it might possibly have been overlooked, or not 

 thought worthy of mention. It appears definitely to characterize M. grisea as contrasted 

 with M. aestimm. 



On the whole I consider that the differences between these four forms, especially in 

 the spermathecal apparatus, and in a somewhat less degree in the testes, penial body and 

 associated structures, and in the copulatory glands, are sufficient to justify their separa- 

 tion. They form a closely related group, but I cannot arrange them in a series showing, 

 for example, a progressive evolution or regression of the distinctive characters according 

 to distribution from west to east or vice versa. On the whole the group appears to be a 

 primitive one ; the testes show the first stages, but only the first stages, in the evolution 

 of the condition characteristic of the genus Lumbricilhis, and the lumbricilline penial 

 body is either absent or present in a very indefinite form; the prostates, however, are a 

 special development, not ordinarily found either in Marionina or Lumbricilhis. 



For the worms described by Benham (1922) I propose the name M. benhami. 



The difference between the two genera Marionina and Lnmbricilltis lies in the testes — 

 massive in Marionina and not divided to the base, divided in Lumbricilhis and forming 

 numerous pear-shaped lobes attached by their narrow ends, each enclosed in a mem- 



