| OCR Text |
Show 232 ME. F. E. BEDDAED ON NEW EAETHWOBMS. [Mar. 19, this part of the world. It appears to be a very southern Patagonian form. It occurs in fresh water as well as upon dry land, as is also the case with Acanthodrilus pictus and a few other worms. The species is long and slender, and is quite bleached by the alcohol. A typically sized specimen selected for measurement was 85 m m . long by 3 m m . broad, and consisted of 92 segments. The prostomium is continued for some way over the buccal segment by grooves, but these do not reach the end of that segment. The setae are more paired ventrally than laterally, the distance between any two lateral setae being about twice that between the ventral setae. The clitellum occupies segments xiii.-xvi. and is quite complete. The nephridiopores open in front of seta 3. The oviducal pores lie exactly in line with seta 1. The most characteristic external feature in the organization of this worm is afforded by the male pores. These pores in the present genus are, as a rule, very conspicuous, but are more or less rounded orifices confined to the xviith segment. In Microscolex michaelseni the male apertures are represented by crescentic slits, which commence upon about the middle of the xviith segment and extend back to at least the posterior extremity of that segment, and sometimes even encroach upon the xviiith segment. This groove is wider in front than behind. A n investigation of it by means of transverse sections showed that the spermiducal glands and the penial setae opened in common at the anterior end of tbe groove where it is widest. The sperm-ducts open at the posterior end. In this wide separation between the external apertures of the sperm-ducts and the spermiducal glands, the present species resembles Microscolex (Rhododrilus) minutus. It will be observed also that the present species is almost an Acanthodrilid in the relations between these organs. The only actual difference between the Acanthodrilidae and the Cryptodrilidae which is invariable, is that in the one (Acanthodrilidae) the sperm-ducts open a segment behind or in front of the spermiducal glands; in the Cryptodrilidae, on the other hand, if the two apertures are separated, they are upon the same segment. In Microscolex michaelseni, however, in some specimens at any rate, the apertures must be at least only just not upon consecutive segments, and in other specimens the groove extended well into segment xviii. O n segments xvii., xviii. are a pair of rounded papillae which lie just behind the furrows, separating these segments from the one in front. Sometimes the anterior pair are closer together than the posterior. The alimentary canal is not provided with a well-developed gizzard ; there is a rudimentary one only in segments vi., vii. The oesophagus gradually passes into the intestine, which acquires its full calibre in the xvitb. The last pair of hearts are, as is usual |
