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Show 1892.] OF THE GENUS PERICHcETA. 165 of a part of the atrium ; the setae are interrupted for a short space on either side of each pore, which, however, lie directly in the line of the setae. I counted seventeen setae between the male pores. I could find no genital or copulatory papillce of any kind. The spermathecal pores were very evident in all the specimens; they lie between segments vii./viii. The dorsal pores commence between segments xii./xiii. The anterior segments of the body are bi- or tri-annulate. With regard to the internal anatomy of the species, I only direct attention to those points which are known to be of importance in the discrimination of species. The position of the gizzard is perfectly normal; it lies in segments viii.-x., and the septa between these segments have nearly entirely disappeared, being represented only by a few ligaments binding the gizzard to the parietes. The intestine is very remarkable on account of the fact that there are no cceca. I looked for these structures very carefully, and entirely failed to discover them ; they are always (according to m y experience) quite easy to find when present. I must therefore conclude that the present species is unique in the absence of caeca. Although there appears to be no Earthworm known on other grounds referable to the genus Perichceta (s. s.) which possesses no intestinal caeca, Mr. Fletcher* has described a Megascolex in which caeca are present. In Perichceta queenslandica, a worm with " interrupted circles of setae," there are a pair of lateral caeca arising from the intestine in segment xxv. and directed anteriorly, as in all true Perichcetce with the exception of Perichceta taprobance 2; these two species evidently render it impossible to define strictly the genera Perichceta and Megascolex, though as a matter of convenience those names may be, for the present at least, retained until more exceptions are made known. In other particulars the alimentary tract of this Earthworm does not diverge from the normal. The intersegmental septa commence to be distinct after the fourth segment ; the first four septa, viz. those bounding segments v.-vii., are rather thickened ; as are also the first two septa which lie behind the gizzard, that is to say those which separate segments x./xi. and xi./xii. The thick septa in front of the gizzard are covered with very conspicuous nephridial tufts. The sperm-sacs lie in segments x., xi., and xii. The atria consist as usual of a thick muscular duct bent upon itself and of a glandular portion consisting of ramifying caeca; the latter is fairly compact except where it is cleft at its junction with the non-glandular part. The glandular part is much smaller than is usual in this genus, and is entirely limited to the xviiith segment. The muscular duct is unprovided with a dilated sac at its extremity. There is only a single pair of spermathecce, which lie in segment viii. They also are small; and, as the facts contained in this account are based upon the dissection of several examples, I may emphasize the 1 " Notes on Australian Earthworms, Part II.," P. Linn. Soc. N. S. W . ser. 2, vol. i. p. 964. 2 I am not certain as to Perich&ta ceylonica. |
