1893.] GENITAXIA OF BRITISH EAKTHWORMS. 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 aucl that no opening into the 

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

 receptaculum ovorum, the contents especially resembling the con- 

 dition figured by Beddard for Perichceta \ At first this structure 

 suggested to my mind the curious rehitions between the oviduct and 

 ovary in Eudrihis ^ ; 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 bv the oblique mesentery. The meaning of the special 

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



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

 various specimens 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 find 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, 

 iu Acanthodrilus, described the ovaries as developed on the posterior 

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



These facts further accentuate the belief in the inherent power 

 of the entire ccelomic epithelium and their derivatives to produce 

 sex-cells. 



These varied positions of the genital glands suggest the con- 

 dition met Mith in many Polychajte worms, ^^■here 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 with in the Oligochseta is the outcome of irregular 

 abbreviation of some such diffuse and possibly hermaphroditic 

 condition under perfected segmentation, rather than of a condition 

 in which the glands were already restricted to definitely metameric- 

 ally arranged centres as in the Planarians. 



The development of the genital glands in the Earthworms has 

 been worked out by Bergh for Lumhncus and by Beddard * for Acan- 

 thodrilus : the latter author describes the constant presence of four 

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

 on the 12th segment ; this gland, however, 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 



1 Q. J. M. S. vol. XXX. pp. 448, 471, pi. xxix. fig. 12 ; see also Bergh, Zeitschr. 

 f. wiss. Zool. Bd. xliv. 1886, p. 318 (footnote) 

 - Q. J. M. S. vol. XXX. and vol. xxxiii. p. 514. 

 3 Cosmovici, Archiv. Zool. Exp. Gen. torn. viii. 1879-80, p. D5','. 

 * Q. J. M. S. vol. xxxiii. p. 497. 



