458 OLIGOCHAETA 



glands open on to the segment in front of and the segment behind this, or if there 

 is but one pair, as in the species Acanthodrilus monocystis alone, they open on to 

 the seventeenth segment; in the.Cryptodrilidae, on the other hand, the termination 

 of the sperm-ducts may be independent of that of the spermiducal glands, but if 

 this is the case the two pores are nearly always situated upon the same segment 1 . 

 Gordiodrilus does not form an exception to this statement ; it is true that here the 

 sperm-duct-pore is independent of that of the spermiducal glands of which there 

 are two pairs opening on to consecutive segments; but one of these opens on to 

 the same segment as that which bears the sperm-duct-pores, whereas in Acanthodrilus 

 the sperm-duct-pore is never upon the same segment as that of the spermiducal 

 glands. Apart, however, from this difference it would be difficult to draw a sharp 

 line of demarcation between the Cryptodrilidae and the Acanthodrilidae. There are 

 no other structural peculiarities in which either family is totally differentiated from 

 the other. I am disposed to agree with MICHAELSEN in considering that Dichogaster 

 is one of the genera which is nearest akin to the genus Benhamia. It will be 

 remembered that in the type-species of the former genus DicJiogas/er damonis 

 there are three pairs of tubular glands of which the two posterior opening on to 

 the eighteenth and nineteenth segments are the smaller, and the anterior pair in 

 common with which open the sperm-ducts are distinctly the larger ; if we suppose 

 the middle pair of these to disappear, and the sperm-ducts to be continued on to 

 the eighteenth segment we should have an Acanthodrilid at once. 



Another point of resemblance, to the Acanthodrilidae is to be seen in Microdrilus 

 saliens and in Ocnerodrilus; in the former worm the buccal cavity has, as I have 

 mentioned in my account of the anatomy of this species, a diverticulum, which is of 

 a different structure to the alimentary tract of which it is a diverticulum ; the cells 

 are more glandular and stain but feebly in carmine ; MICHAELSEN, HORST, and I 

 myself have described in various species of Benhamia a perfectly similar diverti- 

 culum; the description which HOKST has given of this diverticulum of the buccal 

 cavity in the species Benhamia malayana (17, p. 36), which I have already 

 referred to in considering the anatomy of the alimentary canal in the Oligochaeta, 

 shows its identity with that which I have seen in M. saliens; as a matter 

 of fact, however, I have had the opportunity of comparing the structure in 

 question for myself in B. crassa, and can, therefore, certify to its exact similarity ; 

 in both Microdrilus, and in, at any rate, one species of Benhamia, : i. e. that 

 which has only just been mentioned, the end of the sperm-duct, near to its 

 external pore, is enveloped in a thick layer of muscular fibres ; the same thing 



1 Microscolex modestus is an exception. 



