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Show 1892.] ON THE GENUS PERICH^LTA. 153 4. O n some Species of the Genus Perichceta (sensu stricto). B y F R A N K E. B E D D A R D , M.A., Prosector to the Society. [Received February 5, 1892.] (Plates IX. & X.) I have already communicated to this Society 1 some observations upon the family Perichsetidse and upon the generic types which may be recognized in it. In the present paper I propose to describe some species of Perichceta (s. s.). I regard those Perichsetidse as referable to the genus Perichceta in the strict sense in which the setae are disposed in a perfectly continuous circle round each segment, being generally (? always) disposed along a distinct ridge in the middle of the segment; this gives to the species of the genus a very different feel from either Megascolex or Perionyx, since the setse necessarily project more and thus produce a roughening of the skin, very perceptible when the worms are handled. M y experience of living Earthworms of the genus Megascolex is limited to the examination of a specimen (as yet unidentified) from the Seychelles. These worms are far more lethargic in demeanour than the extremely active Perichcetce, and it is quite possible that this difference may be general. Another distinguishing character of the genus is the presence of a pair of caeca 2 projecting forwards from the intestine in the xxvith segment. The gizzard, moreover, lies in segments viii.-x. and the septa are wanting which should divide those segments. No true Perichceta is known in which the spermatheca have more than a single diverticulum apiece3. The clitellum never consists (with one exception, P. fece) of more than three segments (xiv.-xvi.), and the oviducal pore is generally, if not always, single and median 4. Most naturalists who have described species of Perichceta have mentioned the number of setae on the segments ; but a segment has generally been selected at random, and frequently no mention has been made of the particular segment chosen. Prof. Bourne points out that it is desirable to count the setae upon more than one segment, and he selects segments v., ix., & xxv. ; he finds " that the 1 " Observations upon an American Species of Perichceta, and upon some other Members of the Genus," P. Z. S. 1890, p. 52. 2 I refer later on in this paper (p. 165) to one exception to this rule. 3 The second " diverticulum," in the form of a pear-shaped pouch, which occurs in Perichceta houlleti does not belong to the same category as the true appendix of the spermatheca; this I have pointed out elsewhere [Q. J. Micr. Sci. vol. xxx. p. 462]. 1 Fletcher has described and figured an Earthworm (" Notes on Australian Earthworms: Part II." ; Proc. Linn. Soc. N. S. W . ser. 2, vol. i. pi. 13. fig. 6 2, aud p. 962), Perichceta queenslandica, which has the internal organization of a true Perichceta, but " intei'rupted " setae and paired oviducal pores; Perichceta darnleiensis, described on p. 966 of the same memoir, appears to be in every respect a true Perichceta, but has also paired oviducal pores. This matter, however, requires looking into again, as Mr. Fletcher suggests a slight doubt as to whether the said apertures are really separate. |