28 



Elementary Zoology. 



bodies attached on either side of the nerve-cord to the septa, 

 which separate segments 9, 10, ir. The ovaries occupy a 

 precisely similar situation in 13. 



Besides these essential organs, which produce respectively 

 spermatozoa and ova, there are ducts which carry off the genital 

 products. Opposite to each testis (but wrapped in certain sacs 

 which will be spoken of immediately) is a much-folded funnel- 

 shaped structure — ^& funnel of the vas defere?is. Each vas deferens 

 is continued into a narrow tube ; the two tubes of each side soon 

 unite to form a single tube, which opens on to the exterior by 



the orifice already referred 



JJ 1 to upon the fifteenth 



segment. Similarly, op- 

 posite to each ovary is a 

 wide and folded funnel 

 — the internal aperture of 

 the oviduct. This opens 

 into the very next segment 

 — i.e. the fourteenth — on 

 to the exterior. When 

 the earthworm is mature, 

 there are a series of sacs 

 developed by growths of 

 septa, termed the sperm 

 sacs, or the vesiculse semi- 

 nales. Of these there are 

 2-4 pairs lying in seg- 

 ments 9, 10, II, 12; and, in 

 addition, in 10, 11 a sin- 

 gle median sac, with which 

 these paired sacs com- 

 municate. Hence there 

 is a considerable space 

 taken up within the seg- 

 ments mentioned. In these sacs lie the testes and the funnels of 

 the sperm ducts. Thus the sperm which ripens in the sacs cannot 

 fail to find its way to the exKrior, when fertilization takes place. 

 A minute body lying on the septum, bounding the thirteenth 



Fig. 13. — Reproductive organs of Lumbricus. 

 The segments are numbered, t, testis ; sp, sper- 

 matheca ; v.sem, sperm sac ; o, ovary ; o', rudi- 

 mentai-y ovary of segment XIl. ; v.d, sperm 

 duct; F, funnel of oviduct ; o.d, oviduct; k.s, 

 egg sac. 



