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Show 804 MR. F. E. BEDDARD AND MISS FEDARB [June 20, segments xix.-xxii.; three of them show only three pairs on segments xix.-xxi.; one specimen has three papillae on segments xix.-xxi. on the right side, and on segments xx.-xxii. on the left, while on both remaining forms one has only three papillae at the right, the other one at the left side of the body on segments xix.-xxi." The spermathecae also are varied. Only one individual had a pair in each of segments vi. and vii. Four others had no spermathecae at all. In the three others they were asymmetrical and as many as 3 and 5 on one side of the segment. As our series of variations is more extensive than those recorded by Dr. Horst, we think that it wall be worth while to record them. It is conceivably a noteworthy point that our specimens come from tbe New* World, but w e do not wish to lay more stress upon this fact than it will bear. The present communication deals with 18 mature examples of an earthworm from British Guiana, which were received through the kindness of M r . Cecil Lilley, and which show conclusively that there is no need for the retention of the species P. acystis. It-seems to be undoubtedly identical with P. biserialis. Tbe worms were so much softened by the spirit in which they were preserved that it seems to be of no great use to give an attempt at accurate measurement of length. To mention that one specimen actually measured 475 m m . would be to give quite an erroneous idea of its size when in a moderate degree of contraction. It may be taken that these individuals were of about the same dimensions as the examples examined by Michaelsen. The number of segments in a fair-sized specimen was 190. The dorsal pores, as in Michaelsen's specimens, commenced between segments xii./xiii. The setae of this species, as already mentioned, are remarkable for the fact that the two on the ventral median line on either side of the nerve-cord are considerably larger than the others. Furthermore, the setae of the anterior segments are all or most of them larger than those on the posterior segments, and in segments v.-viii. the four most ventral setae are larger than the others and increase progressively up to the 7th. The setae appear to be, for the most part, absent upon tbe clitellum; but in one specimen, at any rate, there vyas a single seta on each side of the middle ventral line of the sixteenth segment. The question of seta? upon tbe clitellar segments of Perichceta is one which requires a renewed consideration. It has been common to use the presence or absence of setae as of specific value, but it seems to be possible, from the variations which have been recorded in some species, that setae are really not finally present upon the clitella of mauy species where they exist for a short period after the formation of the clitellum. As development proceeds they drop out. In a selected series of segments the numbers of the setae are as follows-ii. 42, v. 60, x. 76, xii. 64, xvii. 55, xix. 60, xxiv. 60. A few may of course have been omitted owing to their having fallen out and their apertures not noticed. |