STRUCTURE OP TWO NEW GENERA OF EARTHWORMS. 261 



reconstructing this figure from the transverse sections I have 

 put in the intersegmental septa between Segments 12, 

 13, and 13, 14, which I have not actually observed; I 

 imagine that they will be found to be partially absent, as in 

 Hyperiodrilus. The position of the coelomic sacs is also 

 not quite as in nature ; they have been slightly altered to 

 permit of everything being seen in one figure : but these altera- 

 tions do not affect the mutual connection of the various parts ; 

 these are, I trust, accurately displayed in the figure, and also 

 in fig. 36, which represents the apex of the spermatheca [sp.). 

 Comparing the arrangement of these parts in Heliodrilus 

 with that of Hyperiodrilus we find an increase in size of the 

 spermatheca, and a decrease in size of the coelomic sac involving 

 the spermatheca. The latter, instead of forming a complete 

 ring round the oesophagus completely enclosing the sperma- 

 theca on one side, is only developed on one side of the body, 

 and surrounds only the extremity of the spermatheca. The 

 second sac, lying within the dorsal dilated part of the sac which 

 surrounds the extremity of the spermatheca, is peculiar to 

 Heliodrilus, and is an extraordinary structure, concerning 

 the meaning or function of which I can offer no suggestion. 

 The enormous development of the lining cells of the circum- 

 cesophageal sacs of Hyperiodrilus into the similitude of a 

 glandular epithelium is not found in Heliodrilus. It is pos- 

 sible, however, that it is a periodical occurrence which does not 

 happen to have taken place at the time when the only specimen 

 of Heliodrilus that I possess was killed. The reduction of 

 the coelomic sac surrounding the spermatheca not only in size, 

 but also in the extent to which it involves the spermatheca, 

 culminates in Eudrilus, where, as far as I can see, there is no 

 vestige of any perispermathecal sac left. I should like to make 

 this point quite certain, but in any case it is evident that if 

 such a sac does exist, there must be merely traces of it. The 

 question is whether Eudrilus represents the last term in this 

 series of modifications, or whether Hyperiodrilus does; 

 from what we know of the anatomy of the Oligochseta it seems 

 more reasonable to suppose that the development of these 



