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Show 216 MR. F. E. BEDDARD ON A [Mar. 20, is colourless as in all the other species except AS. ehrenbergii, according to Lankester \ it is of a pinkish colour. There are a large number of pairs of nephridia present, while in AS. variegatum there are only three pairs, occupying segments 4-6, They are very readily visible, and the terminal aperture into the ccelom is extremely obvious, lying midway between two successive seta-bundles. The ccelomic aperture can hardly be termed a " funnel," as it is only just perceptibly wider than the rest of the tube. The external orifice of the nephridium is placed close to the median ventral line. Although the segmentation of JEolosoma does not affect the ccelom, there being no mesenteries present, it is clear that the position of the nephridia is such that, were mesenteries to make their appearance, each nephridium would be entirely contained in a single segmerrt ; the external orifice is in fact in advance of the ccelomic aperture (fig. I). This is of some little importance, inasmuch as in Ctenodrilus 2, undoubtedly a near ally of JEolosoma, the single pair of nephridia are entirely contained within the first segment of the body. Again, in Polggordius 3 the funnels of the nephridia, although they come into close contact with the septum which divides the segment containing the nephridium from the one in front, do not actually perforate it. Polggordius is certainly a very primitive Annelid; and since the same conditions obtain iu the Capitellidse and other Chretopods, there are some reasons for believing that the restriction of a nephridium to a single segment is primitive. On the other hand, it is almost universally the case among the Oligochseta that the funnel lies in the segment in front of that which bears the external aperture of the nephridium. Again, the nephridia of ASolosoma are, as has been pointed out by Vejdovsky, attached to the parietes by simple unicellular muscle-fibres. This is perhaps to be looked upon as a primitive arrangement, since the embryonic nephridium of Allolobophora is, according to Lehmann, attached in a similar fashion*. The characters of the funnel are important ; so far as I can ascertain from a single fortunate section (fig. 4) it is composed of only two cells ; there are at any rate only two nuclei present, and one of these is rather in advance of the other. It is a fact which favours some views which I have put forward elsewhere0, as to the origin of the Annelid from the Platyhelminth excretory system, that in this primitive segmented worm the nephridial funnel should be, at most, two-celled. As to the structure of the nephridia, they consist, as in all Oligocheeta, of " drain-pipe cells." The difference in the number of the nephridia between the individuals which I have examined and those which Vejdovsky has 1 Linn. Trans, vol. xxvi. 1869. 2 The most recent paper known to me on this worm is by Dr. Scharff. Q. J. M. S. vol. xxvii. n.s. 3 Fauna und Flora des Golfes von Neapel, xiv. Monograph of Polggordius, by L. J. Fraipont. 4 Jen. Zeitschr. 1888, pi. xx. fig. 7. 6 Q. J. Micr. Sci. 1888, pt. i. |
