Page:The Zoologist, 4th series, vol 1 (1897).djvu/181

Rh yellow; in others, as the Mucous Worm, it is white; while the Red Worm yields two-thirds of colouring matter.

Mr. Beddard, in his invaluable 'Monograph of Oligochæta,' unfortunately leaves the subject almost untouched. He says (p. 13): "The cuticle seems undoubtedly to be a formation of the packing cells of the epidermis; the pores upon its surface are the outlets of the gland-cells, and their existence appears to be simply due to the fact that the gland-cells do not secrete a cuticle like the other cells, their secretory activity being taken up in the formation of the granules with which they are laden; hence at the points where they abut upon the cuticle there are gaps—the pores in question." In discussing the question of the cœlom—a subject which has been somewhat fully treated by Mr. Lim Boon Keng, Straits Settlements Scholar, since the 'Monograph' was published—Mr. Beddard again (p. 30) introduces the dorsal pores, and as the paragraph represents the latest results, it will be well to give it almost in extenso. "The cœlom," we are told, "is placed in communication with the external medium in a large number of the Oligochæta by a series of pores, one to each segment; in addition to these structures, which are called the dorsal pores, there is, in a certain number—most of the aquatic Oligochæta—a single pore on the prostomium, which is generally spoken of as the head pore" (and is found in the embryo Lumbricus (p. 32), though not in the adult). The dorsal pores are never developed upon the first one or two segments of the body, and the point where they commence is characteristic for the species. The dorsal pores were considered at one time to lead into sacs, the function of which was believed to be respiratory; it is now known that the pores are simply perforations of the integumental layers just at the anterior boundary of the segment to which they belong; there is no lining of epithelium, as has been erroneously stated to be the case; there is simply a discontinuity of the muscular and epidermic layers where the pores exist. The structure of these pores has been more particularly studied by Ude. Their structure in Fridericia has been studied by Vejdovsky and Michaelsen: "in these Worms the pore is bordered by large round glandular cells on each side; no such cells are visible in the case of the dorsal pores of Earthworms. We are at present completely in