1S92.] OF THE GENUS PERICH^TA. 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 may be described which have no existence or 

 important facts in distribution may be ignored. At present there 

 are only two coloured figures of Perichaetidse extant on which any 

 reliance can he placed : these are Bourne's figure of Meyascolex 

 cceruleus and my own of Perichceta indica '. Several coloured 

 figures accompany Schmarda's descriptions of Perichcetce in his 

 ' Neue wirhellose Thiere,' but these are not so useful as they would 

 be if the descriptions were sufficiently full to render identification of 

 the species possible ^. 



The chief internal characters which show variations are the 

 spemiathecse and the atria. The number and position of the 

 sperniathecse, 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. 1 .59). 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 common ; 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 iiicHned to think that the existence of the two pairs of these 

 structures placed in segments xiii. and xiv. will prove to be charac- 

 teristic, not of particular species, but of the genus itself. 



? Perich^ta sumatrana, Horst. 



Megascolex sumatrana, Horst, Notes Leyden Mus. vol. v. p. 189- 

 Perichceta sumatrana, Horst, Midden-Suuiatra, Vermes, p. 5. 

 I have examined five or six specimens of this species, which has a 



1 Vaillant's figure of " Megasaolex diffringens " may be FerichcEta indica. 

 ' Since the above was written I have received, through the great kindness of 

 Prof. Glaus, these worms for identification. 



