1893.] GEiaiALIA OF BRITISH EARTHWORMS. 323 



cover of that ventral oblique septum running back from mesentery 

 12/13 and situated just below the ovary (Plate XXIV. fig. 7). Save 

 that this capsule was non-vascular and that no opening into the 

 coelom could be discovered, it was very suggestive of an additional 

 receptaculum ovorum, the contents especially resembling the con- 

 dition figured by Beddard for Pericliceta \ At first this structure 

 suggested to my mind the curious relations between the oviduct and 

 ovary in Endrihis ^ ; but most careful examination of a complete 

 series of sections failed to reveal a trace of any exit from the ova, 

 the cavity of the capsule being closed on all sides. One was thus 

 forced to the conclusion that the organ was merely a ventral ex- 

 tension of the germinal epithelium shut off from the rest of the 

 ovary by the oblique mesentery. The meaning of the special 

 cavity and capsule surrouudiug this body I am unable to explain. 



One of the most striking facts arising out of the study of these 

 various spechnens is the very marked potentially reproductive 

 character of the posterior faces of the mesenteric septa, especially 

 Nos. 9/10-13/14 ; for we have seen that it is not at all uncommon 

 to fijid genital glands de^-eloped on all these, and occasionally even 

 on the next 3 or 4 septa following. As a rule, the germinal epi- 

 thelium is only developed on the anterior wall of each segment 

 {i. e. on the posterior face of the mesentery) ; but Beddard " has, 

 in Acantliodriliis, described the ovaries as developed on the posterior 

 waM of the segment (anterior face of the mesentery). 



These facts further accentuate the belief in the inherent power 

 of the entire coelomic epithelium and their derivatives to produce 

 sex-cells. 



These varied positions of the genital glands suggest the con- 

 dition met with in many Polychaete worms, where the genital cells 

 are developed from a more or less continuous band of tissue, situated 

 either on the ventral side of the body-cavity, on either side of the 

 nerve-cords, or close round the ventral blood-vessels^. And it 

 seems highly probable that the varying distribution of the genital 

 glands met \\ith in the Oligoeha'ta is the outcome of irregular 

 abbi'eviation of some such difFuso and possibly hermaphroditic 

 conditiou under perfected segmentation, rather than of a condition 

 in which the glands were ah'eady restricted to definitely metameric- 

 ally arranged centres as in the Plauarians. 



The development of the genital glands in the Earthworms has 

 been worked out by Bergh for Lumhricus and by Beddard ' for Acan- 

 thodrilus : the latter author describes the constant presence of foiu* 

 pairs of gonads in the embryo, the additional pair being situated 

 on the 12th segment ; this gland, liowever, never attains any sexual 

 differentiation and disappears early, so that only three pairs of 

 gonads are found in the adult. This rudimentary pair of glands 



* Q. J. M. S. vol. XXX. pp. 448, 471, pi. xxix. fig. 12 ; see also BergL, Zeitscbr. 

 f. wiss. Zool. Bd. xliv. 188G, p. .'518 (footnote) 



'■* Q. J. M. S. vol. XXX. and vol. xxxiii. p. 514. 



•' Cosmoviti, Arcliiv. Zool. Exp. Gen. turn. viii. 1870-80, p. 357. 



* Q. J. M. a. vol. xxiiii. p. 497. 



