216 OLIGOCHAETA 



from some part of England ^, but cannot give any details. There is every probability 

 that it is a native of this country. 



The most salient external character of the genus is the long prostomium ; the 

 peculiar form of this is sufficient to prove that Hoffmeister and Grube were 

 dealing with the same worm in their descriptions of Rkynchelmis and EiMxes; the 

 same kind of prostomium occurs also in the nearly-related genus Sutroa from North 

 America; but nothing of the kind is found in any other Lumbriculid; in Nais 

 proboscidea, however, there is a prostomium which is of the same character. 



The nephridia are, of course, paired structures ; they commence in immature 

 individuals in the seventh, in mature individuals in the twelfth, segment. The 

 nephridia become enormously large in proportion to the worm ; they stretch so 

 far back beyond their point of opening that, 'on a supei"ficial inspection each 

 nephridium has the appearance of occupying several segments.' The nephridiopores 

 are placed in front of the ventral setae. 



The vascular system of Rhynchelmis is described in some detail in Vejdovsky's 

 original paper upon the anatomy of the worm ; a good figure of some additional 

 particulars is to be found in the Entwickelungsgeschichtliche Untersuchungen 

 (PL xxviii. figs. 7 and 8). The dorsal vessel is pulsatile; it communicates with the 

 ventral vessel by a series of perivisceral trunks, a pair to each segment; after the 

 eighth segment there are, in addition, a pair of vessels arising from the dorsal trunk, 

 which do not end in the ventral vessel, but give oiF a number of contractile branches, 

 as in other Lumbriculidae ; there are six or eight pairs of these branches, which 

 were confused by Grube with diverticula of the gut; when the worms have 

 attained to sexual maturity, the ninth, tenth, |tnd eleventh segments, are seen to 

 contain each a pair of long vessels, giving off a rich network, which ramifies over the 

 sperm-sacs and the other reproductive organs ; the intestine has a rich plexus, derived 

 from the paired, non-contractile perivisceral trunks. The ventral vessel consists, in 

 the first five segments of the body, of two separate halves, each half receiving the 

 perivisceral trunk of its own side. 



The testes, at first overlooked by Vejdovsky, were subse(][uently (9) recognized 

 by him as two pairs of gonads in the ninth and tenth segments ; as the worm gets to 

 be mature, the testes disappear, their contents being transferred to the sperm-sacs ; 

 the same thing happens to the ovaries, which lie in the eleventh segment. The 

 spei-m-sacs have been already described in sufficient detail (p. 93). The spermathecae 

 and the sperm-ducts open behind the ventral pair of setae of their segment; the 

 albumen gland opens in the middle line, between these setae ; the oviducal pores are 



' I believe this specimen to be in the Oxford Museum. 



