BAETHWOKMS. 81 



but setae as organs of locomotion ; no oral armature, cirri, ten- 

 tacles, or branchisB. They are hermaphrodites, and develop 

 direct. 



The Oligochaetse are again divided into (a) the Terricolce, or 

 true earthworms, with nephridia in the genital segments ; and 

 (b) the lAmicolcB, or water- worms, which have no nephridia in 

 the genital segments (Naidce). 



Life-history of the Earthworm {Lwmbricus terrestris). — The 

 eggs of the earthworm are laid in heaps or capsules in the 

 ground. In one or two weeks these white transparent eggs give 

 rise direct to young Lumbrici, which are at first soft, but as they 

 grow they obtain a compact skin armed with setae in simple pits 

 and have red blood. Eyes are never present, yet worms are very 

 susceptible to light. Each capsule is filled by several ova, plus 

 the sperm from the male receptacle. As a rule, only one ovum, 

 or a very few at least, develop ; the others die and shrivel up, 

 unless eaten, as they often are, by the embryo that hatches out. 

 This embryo eats not only the others, but it takes up all the 

 common mass of albumen. It then bursts its way out of the 

 capsule as a perfect worm, minus its sexual organs. Earthworms 

 grow by fresh segments being added posteriorly. In the mature 

 female we get two ovaries in the thirteenth segment and two 

 oviducts in the same, commencing in two ciliated funnels and 

 opening to the exterior in the fourteenth segment. On the 

 ninth and tenth segments are two pairs of sperm-reservoirs, the 

 receptacula seminis, which open between the ninth and tenth 

 and tenth and eleventh segments. These are full of sperm 

 during copulation. 



The male organs consist of two pairs of testes in the tenth and 

 eleventh segments, opening by an aperture on the fifteenth. In 

 the anterior half of the worm, over these sexual organs, is formed 

 in the breeding season a swollen band called the clitellus. 

 Earthworms, although hermaphrodites, copulate : this act takes 

 place at night on the surface of the earth in June and July 

 to the greatest extent. The worms apply themselves ventrally 



F 



