| OCR Text |
Show 1894.] NEW GENERA OF EARTHWORMS. 383 two couples of each side, while the ventral couple of one side is separated from its fellow of the other side by a distance of 2-5 m m. I could not find any trace of setas at all upon the first five segments of the body. If this absence of setae upon the head end be confirmed it is of interest, as this cephalization is rare among the Cryptodrilidae, though a common character in the family Greo-scolicidae. Geodrilus in fact is the only Cryptodrilid in which I can recall anything of the kind. Segments vii.-xii. are bi-annulate. The dorsal pores are very obvious. They commence on the borderline of segments x./xi., possibly one or two segments earlier. There are three of these pores upon the clitellum-one marks its posterior boundary, while two lie on the first two segments. The clitellum is rather extensive, occupying segments xiii.-xxii. The median ventral region behind the male pores seems to be free, at any rate to a large extent, of glandular tissue. The two male pores lie upon segment xvii.; they are highly conspicuous and are transversely elongated orifices, which correspond in position to the missing veutral setae of the segment. Neither the oviducal nor the spermathecal pores were visible. The body-wall of both the present species and Millsonia nigra is exceedingly tough. Mr. Millson informs m e that this was also the case during life. Vascular system.-The dorsal blood-vessel of the worm is single from end to end of the body. In segments xvi. and xvii. it is distinctly dilated, forming thus a kind of heart. A local dilatation of the dorsal vessel is not unknown, though rare, among the Oligochaeta. In the Geoscolecid Microchceta I and Benham have described the same kind of thing, while many Enchytraeids also show a dilatation of the dorsal blood-vessel just after its emergence from the peri-intestinal sinus (or plexus). I regard all these local expansions of the dorsal blood-vessel as having some relation to the heart of the Arthropods. The last pair of circumcesophageal trunks are in segment xii. ; the five pairs which lie in front of these are equally large. Inter segmented Septa.-The first distinguishable septum lies between segments iv./v. It is tolerably stout and runs in a straight course across the body. The four following septa are excessively delicate and are pushed back by the stout gizzards so as to have lost their definite relation to the segments which they separate. After these thin septa come a number which are very strong and muscular. The septa dividing segments ix./xvii. are stout, diminishing in thickness posteriorly. The anterior of these and those which lie in front of them as far back as septum xiv./xv. are traversed by or give rise to muscular straps which are also attached to the parietes and to the alimentary canal. Nephridia.-I do not give a long account of the nephridia under the present species as they are constructed upon the same plan as those of Millsonia nigra, in which species it so happens that I investigated them more closely. The peculiarity of the nephridia of this genus, to which I have already referred, is not quite so strongly marked in the present species as it is in the next to be described. |
