OCR Text |
Show 1892.] OF THE GENUS PERICHcETA. 171 The atrium is not provided with a terminal sac ; the glandular part of each atrium is very extensive, and reaches from segment xvii. to segment xxii. Between the opening of the atrium and the nerve-cord on each side of the body are three small white oval glands (p-g-, fig« 6, Plate X.), which correspond to the papillae visible on the exterior of the xviiith segment. Note on a Perichaeta from Singapore. I received a single specimen of this Perichceta in a living condition from Kew Gardens; it had reached there in a Wardian case from Singapore. Unfortunately I omitted to make any notes upon the worm while alive ; a quantity of other material which came about the same time obliged me to preserve it at once for future study ; the specimen was killed in Perenyi's solution and investigated by means of transverse sections. It is very possibly the same species as that which I have called Perichceta morrisi, and described in the present paper ; but my notes upon its diagnostic characters are so far from being complete, that I do not venture to express an opinion as to the name which should be applied to it. It measured 2\ inches when preserved. The clitellum occupied the usual three segments, but I am not certain as to whether setae were, or were not, present. On the xviiith segment was a single median papilla placed between the two atrial pores. I observed the gizzard to occupy the usual position and that cceca were present. There are two pairs of spermathecce in segments vi. and vii.; these agree very closely with those of Perichceta morrisi in the proportions of the appendix to the spermatheca, but the extremity of the former was swollen, forming an oval sac. This is possibly merely due to the presence of more sperm in one case than in the other. I desire to call special attention to the structure of the atria. These organs have the usual form characteristic of the genus Perichceta. Their minute structure, however, presents one character of some little interest, which has not yet been recorded in the genus. Transverse sections through the stout muscular duct by which the secretions of the glandular part of the atrium reach the exterior show that the muscular sheath encloses three separate ducts instead of only one, as is the case in all other species which have been as yet investigated microscopically. One of these tubes is large and is the main conduit of the secretion of the gland ; the two other tubes are equal in size to each other, but very much smaller than the main tube. The smaller tubes retain their distinctness from the larger tube until near the external orifice, though still remaining enclosed within the same muscular sheath. Just before the external aperture |