THE DORSAL PORES OF EARTHWORMS. 151 



The most important contribution to the subject is un- 

 doubtedly that which was made a few years ago by Hermann Ude, 

 in a paper which deals chiefly with the structure of the body- 

 wall in Earthworms.* He points out that "the dorsal pore lies 

 on the anterior edge of the somites in which it occurs, and 

 appears on the intersegmental groove. It is absent in the most 

 anterior somites, but the position of the first pore is constant 

 for a given species." In the Common Earthworm it occurs 

 between eight and nine, and in the Turgid Worm between ten 

 and eleven. We should say between eight and nine and nine and 

 ten respectively. Claparede formerly described the epidermis as 

 being folded inwards at the dorsal pore, just as it is where the 

 setae are situated, but Ude shows that such is not the case. By 

 stripping off the epidermis I have been able to detect the in- 

 folding of the cuticle around the setae, but not around the dorsal 

 pore, which, as Ude affirms, is a perforation through the epi- 

 dermis and the muscular layers. The pore is wanting in most 

 Freshwater Worms or Limicolce. Beddard has dealt with the 

 exceptions. In some worms, when the girdle is fully developed, 

 the pores become closed through the growing up of the cuticle 

 around the edge. This is not always the case, however, for the 

 Mucous Worm has been noted by some to be an exception, while 

 I have found that the dorsal pore on the clitellum or girdle 

 of some species is quite as discernible after the organ has 

 attained full development as before. 



If a worm is opened laterally, and the internal organs 

 removed so as to leave only the body-wall, it will be possible so 

 to display this portion of the animal as to see the whole series 

 of pores in regular succession. It will be easy then to observe 

 that they are connected with each other by a kind of tube which 

 runs right along the back of the worm. I am a little doubtful 

 whether or not this is what Ude refers to when he says that the 

 epithelium of the body cavity passes across the muscular layers, 

 and meets the cuticle around the edge of the pore. The pore has 

 a special set of muscle-bundles which form its sphincter muscle. 



Ude does not think there is the slightest connection between 

 the pores and the nephridia, which are excretory in their function. 



* Zeit. f. Wiss. Zool. xlvi. pp. 85-142. Benham, Q. J. Mic. Sc. Aug. 

 1886, No. cv. pp. 102-4. 



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