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Show 154 MR. F. E. BEDDARD ON WORMS [Feb. 16, relation of these numbers to one another varies with other important characters rather than the actual numbers themselves." Prof. A. G. Bourne' considers that in all true Perichceta there are setae between the male pores. So far as m y own experience goes I agree with Prof. Bourne. The only possible exception that occurs to me is Perichceta taprobance described in the present paper (on p. 163). That species has setae between the male pores, but differs from Perichceta in a few other points to which I direct attention. Another point which appears to m e to be of importance is the size of the setae upon the anterior as contrasted with the posterior segments ; in all the species of Perichceta described in the present paper the setae of the eight anterior segments are very much larger than those upon the segments which follow ; there is an abrupt break at the end of segment viii.; up to this point the setae get gradually larger upon successive segments. In Perichceta taprobance, which may perhaps be a distinct genus, there is no such marked difference between the segments in front of and those behind the eighth. Although there is a sudden diminution in size of the setae there is not always a corresponding increase in their numbers, but there <>enerally is an increase. So much, then, for the generic distinctions of Perichceta. As to the species there exists already some little confusion, and I am not prepared to guarantee absolutely the novelty of the species described in the present paper. When there were only a very few species of the genus known, their discrimination was a much easier matter than it is now; at the time that Perrier wrote his first descriptions of Perichmtce it was a nearly sufficient definition to state merely the number and position of the spermatheca?. There are therefore a good many points, now known to be of systematic importance, which are omitted or not clearly set forth in some of the papers which record new species of Perichcetce. So far as we know at present, the following are the principal external features which are of systematic importance :- (1) Whether the ventral setae are larger than the rest. (2) The number of setae upon the segments. (3) Whether the clitellum includes the whole of segments xiv.- xvi.2 (4) Whether the setae are present or absent from some or all of the clitellar segments; and if present wdiether they are modified (as, for instance, in Perichceta houlleti). (5) The number and arrangement of the anterior and posterior genital papillae. (6) The position of the atrial pores upon the xviiith segment, i. e. whether they are more lateral or ventral. (7) Colour and size (including number of segments). I should like to take this opportunity of calling attention to the importance of illustrating these and other Earthworms by accurate 1 " O n Megascolex ccertdeus, Templeton, &c," Q. J. Micr. Sci. vol. xxxii. 2 M y attention was directed to the importance of this point by Prof. Bourne's paper upon Megascolex cceruleus (Q. J. Micr. Sci. vol. xxxii. p. 49), |