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Show 142 DR. W. B. BENHAM ON [Feb. 16, out that the numbering of the somites, as it stands in m y description, requires some alteration, and Beddard 1 t has likewise made certain corrections in regard to the interpretation of certain organs, which have become necessary from the advance in our knowledge of the anatomy of the group2. I here give a figure (Plate VIII. fig. 8) of the anterior end of M. beddardi, in illustration of my remarks on the alteration of numbering of this somite. Microchceta papillata has a length of 10 inches and a breadth of half an inch ; it is thus smaller than either of the two previously known species. As to its colour, I am unable to speak, for, as is so generally the case, it has evidently been considerably changed by the spirit. The prostomium (Plate VII. fig. 5) is, as in M. beddardi, broad and marked by longitudinal grooves, which extend into the first somite (cf. Plate VII. fig. 6, representing M. belli) ; this somite is similarly grooved on the ventral surface. The following somites are bi- or tri-annulated, but the grooves between the annuli are in some cases almost as marked as those between the somites, so much so, indeed, that in fixing the position of the various external characters I at first reckoned the annuli as somites. The first three somites are not annulated ; the fourth to the ninth inclusive are bi-annulated (a, b), the grooves between the annuli being very deep ; posteriorly the somites are not so noticeably annulated. This same well-marked annulation of the somites exists, as I have pointed out and figured, in M. rappi. The chcetce, however, serve to define the somites, and, as in the other two species, are in four couples per somite, the individuals of a couple being close together; the outer couple is quite lateral in position, being about midway between the dorsal and ventral median lines; whilst the inner couples are latero-ventral. The interspace between the outer and inner couples is about equal to the space between the two inner couples. The chaetae themselves are very small, and in the anterior somites, indeed, I had to make use of Zeiss's B, as a hand-lens, in order to see them ; they commence in somite iii. It might be suggested that the first somite is biannulate, but in M. belli (Plate VII. fig. 6) the chaetae occur in the second somite, which is in other respects similar to the second ring of the present species. The four species exhibit an interesting series of stages in " cephalization." In M. belli the first and second somites are distinct, the chaetae being present on the latter. In M. beddardi these somites are not distinctly marked off from one another (Plate VIII. fig. 8), and the apparent first somite carries chaetaa in its hinder part; in M. papillata, though the somites are distinct, the chaetae are absent on the second: in M. rappi the two somites are with difficulty distinguishable from one another; the first annulus 1 " The Classification and Distribution of Earthworms," Proc Rov Phvs Soc Edinb. x. pp. 242, 243. J' * ' 2 Eosa points out this necessary correction in the paper just referred to on p. 384. |