OCR Text |
Show 1892.] OF THE GENUS PERICHCETA. 167 The atrium is not furnished with a distal sac. There are two pairs of spermathecce, which lie in segments vi. and vii • the appendix is a tube of uniform calibre and is very nearly as long as the pouch. In the case of one spermatheca, the appendix is twisted at its commencement round the stalk of the spermatheca. PERICHCETA BARBADENSIS, n. sp. Iu June of the present year I received from Kew Gardens five livino- worms of the genus Perichceta, which were all of a reddish-brown colour with a grey clitellum ; the iridescence of the cuticle was very marked, on account of the dark pigment in the body-wall ; when the worms were killed in weak alcohol, a quantity ol yellowish fluid was expelled from the dorsal pores. In spite of the close similarity in colour between all five specimens, I believe that they are to be referred to two distinct species, of which one_that which I call Perichceta barbadensis-is somewhat protean, showing considerable variations, which I do not, however regard, for reasons which will be stated presently, as being of specific value. I describe the second species subsequently (see p. 169). Two of the specimens were of about the same size, measuring 41 inches in length (when preserved in strong alcohol, after having been killed in weak alcohol) ; the diameter in front of the clitellum is 4 m m The length of the preclitellar somites is 18 mm.; the clitellum itself measures 4 mm. The number of segments is 78. ,, In this individual-which I call a-setae were present upon the last segment of the clitellum (Plate IX. fig. 6) ; the clitellum itself in all three specimens is fully developed upon all the segments xiv.-xvi. and bears anteriorly the single median oviducal pore; the number of setae upon the last segment of the clitellum is small, about halt a dozen. • ,, . In the second individual (6) the number of setae upon the last segment of the clitellum is greater than in a. In the third individual (c) the number of setae upon the last segment of the clitellum is about as great as in b, but in addition the first segment of the clitellum (i. e. no. xiv.) bears three, or possibly four, setae on each side of the oviducal pore (Plate IX. fig. 7), which there lies within the circle of setae of its segment, and not, as is usually the case in the genus Perichceta, in front of the setae. It might be supposed that these three individuals represented merely three stages in the disappearance of the setae belonging to the clitellar segments. In immature worms setae are always present upon the clitellar segments. I am not aware that any exact observations have been made as to the time and manner of their disappearance in those species which have, when adult, a clitellum devoid of setae. But in the present species the differences in the clitellar setae coincide with differences in the genital papillae and also with differences in the number of spermathecae. But, as will be seen presently, it does not happen that the worm with the fewest setae upon the clitellum has the most marked development of the genital papillae. Hence I |