324 ON THE GENITALIA OF BRITISH EARTHWORMS. [Mar. 28, 



is evidently the homologue of the additional gonads on the 12th 

 somite described above in the adult Allolobo2)7wra and Idimbnais ; 

 and I believe that when we know more of the development of 

 other Earthworms, this additional pair of gonads will be found to 

 be present in most of them at one stage of their existence. 



In three very young worms (L, terrestris ?) I found this pair of 

 gonads present, and I think that Bergh possibly overlooked it in his 

 account of the development of the genital glands, as, from the 

 number of adult specimens of Lumbrims and Alloloboplwra in 

 which I have found this pair of gonads, I think that it is in all 

 probability always developed in the embryo, as in AcantJiodrilus, 

 but generally disappearing in the adult. 



The receptacula ovorum were in this specimen, and as I have 

 frequently observed in other AUolobojyhom, totally disconnected 

 from the oviduct ; in fact, if the development of the former be 

 studied (as can easily be done in young worms) they may be found 

 to arise as outgrowths of that portion of the coelomic epithelium 

 covering the anterior face of mesentery 13/14, dorsal to and quite 

 independent of the oviducts, whose cihated epithelium may sub- 

 sequently extend up to their openings. To represent these recep- 

 tacula ovorum as outgrowths of the oviducts is, I think, erroneous 

 and misleading, as they are the homologues of the seminal vesicles ; 

 and, like them, they ai'ise as hollow outgrowths of the mesenteric 

 septa, and their connection \ntli the oviducts (when effected) is a 

 secondary one. 



EXPLANATION OF PLATE XXIV. 



Fig. 1. Longitudinal vertical section of an abnormal AUolohophora longa, X20. 



t^, posterior testis ; /, seminal funnels ; h, hermaphrodite gland ; ov^, 



ov^, ovaries ; ovd, oviduct ; m, mesenteric septa ; s.o, segmental organ ; 



n, nephrostome ; o.m, oblique mesentery ; c.v.d, coiled portion of 



vas deferens. 



2. Right additional genital gland (testis) from segment 12. 



a. Entire gland clarified, x20. 



h. Part of free end, X 320 ; m, mulberry-shaped masses of developing 



spermatozoa. 

 c. Portion showing bundles of ripe spermatozoa (sp). 



3. Base and apex of normal testis, X 320: s, typical sperm mother-cell 



enlarged. 



4. Hermaphrodite gland from segment 12 : ov, ova ; s^j, young sperm 



mother-cells, x320. 



5. {a) Base of normal ovary, X640; {h) single ripe ovum with archo- 



plasm, x320. 



6. Additional ovary from segment 14, X 320. 



7. Mass of ova (? ovary) from below the oblique mesentery {o.m) oi seg- 



ment 13 : c.jo, epitheloid capsule, xUO. 



