THE DOBSAL POEES OF EAETHWOEMS. 153 



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 Oligocheeta,' 

 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 

 coelom — 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) intro- 

 duces the dorsal pores, and as the paragraph represents the latest 

 results, it will be well to give it almost in exienso. " The 

 coelom," we are told, "is placed in communication with the ex- 

 ternal medium in a large number of the Oligochaeta 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 Oligochscta — 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 con- 

 sidered 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 



