2 o6 DESCRIPTIONS OF PREPARATIONS. 



pairs of vesiculae seminales, and a paired vas deferens. The testes are situated 

 near the nerve cord on the posterior faces of the anterior septa dividing the tenth 

 and eleventh somites. Each testis is described by Blomfield as ' a white trans- 

 lucent body of irregularly quadrangular form, rarely more than one-tenth of an inch 

 in diameter, much flattened, and attached by one side to the coelomic epithelium of 

 which it appears to be a local modification.' In the Chaetogastridae the spermato- 

 zoa begin to develope in the coelome and complete their growth in the sperma- 

 thecae, but in most Oligochaeta, as in the Earthworm, they develope in vesiculae 

 seminales which are caecal outgrowths of the septa. This is their probable origin 

 in' Lumbricus. The immature vesiculae in this worm are, according to Blomfield, 

 'six small light-coloured vascular growths on the three septa 9-10, 10-11, 11-12, 

 arranged in three pairs.' The first and second pairs are anterior outgrowths of the 

 septa to which they belong : the third is a posterior outgrowth of the septum 11-12 

 (Benham, note, p. 259, Q. J. M. xxvi. 1886). The cavities of the vesiculae are 

 traversed by connective tissue trabeculae and capillary bloodvessels. The sperm- 

 polyplasts and fully formed spermatozoa are lodged in the interstices of the 

 trabeculae, in which may also be found the Gregarine Monocystis Lumbrid in 

 all stages of its life-history. When the Earthworm is sexually mature the first four 

 vesiculae 'form a central body covering in the rosettes and testes of the tenth 

 segment.' A similar coalescence occurs in the eleventh somite between the two last 

 vesiculae. Each vas deferens consists of two ciliated funnels or rosettes ; one situated 

 in the tenth, the other in the eleventh somite, which join a common duct. The 

 latter opens near the ventral set of setae in the fifteenth somite. It therefore 

 traverses three somites. 



The two ovaries occupy a similar position to the testes but are lodged in the 

 thirteenth somite. Each is invested by a layer of flat peritoneal cells. When 

 mature it has the form of a pear with a long stalk the latter being formed of a 

 single string of ripe ova. It consists, when immature, like a testis, of a finely gran- 

 ular protoplasm with scattered nuclei, in other words, of a syncytium. The ova 

 of the aquatic Oligochaeta, e. g. Tubificidae, break away from the ovary and ripen in 

 the coelome or in an ' egg-sac ' similar to the vesiculae seminales. Each oviduct 

 commences with a wide ciliated aperture vis a vis to the ovary. The duct per- 

 forates the septum between somites thirteen and fourteen, and opens in the 

 fourteenth somite near the ventral row of setae. A receptaculum ovorum, or 

 'egg-sac,' is attached to the oviducal funnel and receives the ripe ova. It 

 contains 1-5 ova, and like a vesicula seminalis, it is a diverticulum of a septum, 

 that which separates somite thirteen from somite fourteen. It projects into the latter 

 (Bergh). The female apparatus is completed by two pairs of vesicular sperma- 

 thecae which open in the inters egmental furrows between somites nine and ten, 

 and ten and eleven, and are derived as in aquatic Oligochaeta from invaginations of 

 the hypodermis (Bergh). They receive the spermatozoa in congress and secrete a 

 clear fluid, which, according to Vejdovsky (op. cit. pp. 154-5), forms the spermato- 

 phores. The clitellar glands are usually supposed to form these structures. The 

 spermatophores are 1^2 mm. long and 0-5-0-7 mm. wide, somewhat spirally coiled, 

 and with an open hollow at one end in which the spermatozoa lie parallel to one 

 another. In some worms they are closed. They are usually attached on or about 

 the clitellum. 



