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Show 1892.] OF T H E GENTJS PERICHCETA. 155 coloured figures. The species of Perichceta generally (so far as my experience goes, always) show characteristic differences of colour which it is difficult to express in words so as to convey a sufficiently accurate idea. The characters, moreover, which separate the species of Perichceta are not always available ; some species are separable by very well-marked characters, but others again hardly differ, except in the number and position of the genital papillae with which are associated peculiar glands, and in their colour; immature specimens often want the papillae, and, in the absence of coloured figures for reference, new species m a y be described which have no existence or important facts in distribution m a y be ignored. At present there are only two coloured figures of Perichaetidae extant on wdiich any reliance can be placed: these are Bourne's figure of Megascolex cceruleus and m y own of Perichceta indical. Several coloured figures accompany Schmarda's descriptions of Perichcetce in his ' Neue wirbellose Thiere,' but these are not so useful as they would be if the descriptions were sufficiently full to render identification of the species possible2. The chief internal characters which show variations are the spermathecae and the atria. The number and position of the spermathecae, and perhaps the relative size of the spermatheca and its diverticulum, offer useful characters ; but they are rather difficult to make use of, as the quantity of sperm in the diverticulum is responsible for considerable variations in its form, as I point out in the case of Perichceta sinensis (see p. 159). The atrium is sometimes furnished at its point of opening with a dilated sac, the presence or absence of which is very characteristic of a given species. The extent of the glandular part of the atrium is perhaps often a valid specific distinction, especially in such forms as Perichceta taprobance, where it is extraordinarily small. The intestinal caeca are also subject to some variation, which is, however, not c o m m o n ; in two species only are they absent, and in two others there are six pairs instead of the normal one pair. There seems also to be some variety in the position of the specially thickened intersegmental septa ; but this character is one which is best appreciated in large species such as Perichceta forbesi, and is not always so clearly marked in the smaller forms. Whether the receptacula ovorum really vary from one to two pairs is a matter which requires further investigation. At present I am almost inclined to think that the existence of the two pairs of these structures placed in segments xiii. and xiv. will prove to be characteristic, not of particular species, but of the genus itself. ? PERICHCETA SUMATRANA, Horst. Megascolex sumatrana, Horst, Notes Leyden Mus. vol. v. p. 189- Perichceta sumatrana, Horst, Midden-Sumatra, Vermes, p. 5. I have examined five or six specimens of this species, which has a 1 Vaillant's figure of " Megascolex diffringens " m a y be Perichceta indica. 2 Since the above was written I have received, through the great kindness of Prof. Olaus, these worms for identification. |