i8 9 5. NOTES AND COMMENTS. 373 



Pterodrilus. The family, it should be explained, was formerly referred 

 to the leeches on account of the jaws and the suckers. It is familiar to 

 most zoologists in this country by the genus Branchiobdella. The new 

 genus shows, perhaps even more obviously than Branchiobdella, the justice 

 of placing these worms among the Oligochaeta and of removing them 

 from the Hirudinea. As a matter of fact, the gulf between those 

 two groups is not now by any means so great as it was when we were 

 only acquainted with the anatomy of Lumbvicus among earthworms. 

 There are many worms now known, belonging to the family Eudrilidae, 

 in which the generative pores are single and median, and in which 

 there is a reduction of the ccelom by the extraordinary development 

 of perivisceral sacs surrounding certain of the generative organs ; 

 these to some extent bridge over the gulf which has hitherto lain 

 between the leeches and the earthworms. Pterodrilus is chiefly 

 remarkable for the paired processes upon the back, which clearly 

 suggest gills. There are now quite a crowd of Oligochaeta, which, 

 contrary to the Cuvierian definition of the group, are gilled. Dero 

 has been long known with its circlet of gills round the anus. Professor 

 Bourne has lately made known the Indian Naid, Chcetobranchus, in 

 which there are paired processes of the body-wall, which contain 

 blood-vessels, and in which also, in certain parts of the body, the 

 seta? are implanted. More recently still, Mr. Beddard has described 

 the Tubificid Branchiura, with retractile gills upon the posterior 

 segments of the body, containing blood-vessels, and an extension of 

 the body-cavity separated from the general body-cavity by a dia- 

 phragm. And, lastly, there is the genus Alma, as it was originally 

 called, which Dr. Michaelsen has lately shown to be identical with 

 Siphonogaster . This is a true earthworm, with retractile gills that can 

 be withdrawn into pits upon the body. Pterodvilus has a series of 

 paired outgrowths of the dorsal body-wall which suggest gills ; but, 

 as the author of the paper points out, they do not altogether fit in with 

 what might be expected of a branchial organ, in that they have no 

 blood-vessels ; they have no internal cavity either, but are solid 

 throughout. 



In the male reproductive organs this little Discodrilid is curiously 

 like the aquatic family Lumbriculidas. There are, as in the last- 

 mentioned family, two pairs of sperm-ducts, which open, however, 

 into a common atrium ; in the segment in front of this lies the single 

 spermatheca. Although the terminal gland of the male ducts, which 

 is often termed the atrium, is single in this as in other Discodrilids, it 

 shows traces of division, and there are four male ducts. There are 

 two species of the genus, which, like their European allies, are 

 parasitic upon crayfishes (Cambarus) ; they are of minute size, hardly 

 exceeding a millimetre in length. If there was any doubt about the 

 systematic position of the Discodrilidae after the researches of Voigt 

 and the monograph of Vejdovsky, Mr. Moore's paper settles the 

 matter — at least to our satisfaction. 



