152 THE ZOOLOGIST. 



Yet in a sense the dorsal pores play their part in the excretory 

 process, since the fluid contained in the coelom or body-cavity, 

 as well as certain other substances which in some species 

 of Earthworm are coloured, can be caused to exude through 

 them. Sometimes the exudation is in drops, but some foreign 

 species are able to squirt it to a distance of a foot, much as Peri- 

 patus does. In these cases the process is perhaps protective. 



In a memorable article on the Earthworm, published some years 

 ago, Prof. Ray Lankester * says : " In the cuticle of the Earth- 

 worm a system of very minute canals exists, . . . which might 

 either be described in connection with the respiratory mechanism, 

 or here, if we regard these ducts as excretory pores ... It is 

 undoubtedly through these minute canals, which exist throughout 

 the integument of the Earthworm, that water passes to the peri- 

 visceral cavity, and a dense fluid passes out." Ude tried a series 

 of experiments to ascertain whether or not water was admitted 

 through these pores, but he failed to satisfy himself that sucli 

 was the case, though I have many times observed the denser 

 fluid of which Prof. Lankester speaks issuing from them. 



It is to Prof. Busk that we are indebted, through Prof. 

 Lankester, for one of the best accounts of these apertures in 

 English. In a remarkable paper on the Earthworm, published 

 by the latter in 1865, we have an illustration of the integument 

 of a Worm with all the various pores found on the dorsal surface 

 carefully represented. " One of these orifices, situated in the 

 median dorsal line of the segment, appears always to be larger 

 than the others, and penetrates directly to the perivisceral 

 cavity. That these openings form a very ready and frequent 

 means of escape to the colourless fluid may be ascertained by 

 handling a large Earthworm, when some considerable quantity 

 is nearly invariably found to escape from its dorsal surface." t 

 Nor is this all. Prof. Busk says that the fluid expressed from 

 these pores was of a dirty greyish colour, thin and opaque. 

 Examined under the microscope, it contained numerous spherical 

 particles and pyriform granular bodies, besides irregular organic 

 particles. This coloured fluid differs with the species of Worn 

 examined. In some, as the Brandling and Turgid Worm, it ij 



* Q. J. Micro. Sc. 18G5, pp. 9 and 10, " The Anatomy of the Earthworm.' 

 | Ibid. p. 102. 



