506 ANNELIDA. 



into a packet. They are found on the segments which during 

 copulation are placed opposite to the male genital pores. The 

 tubercula pubertatis are papillae on the ventral side of the clitellar 

 segments. 



The clitellum or girdle is a glandular thickening of the integument 

 of one or more segments of the body. In the Limicolae it is on the 

 generative segments themselves. In the Terricolae it varies in 

 position, but is never in front of the 12th segment, except in the 

 Moniligastridae. 



The male and female openings are on the clitellum in Typhaeus, Megascolides, 

 Evdrilus, Pontoscolex, Criodrilus, Moniligaster, etc. (in Moniligaster the male 

 openings are between 10 and 11, the female openings between 11 and 12) ; in 

 Hormogaster, Diachacta, Rhinodrilus, Brachydrilus, etc., the male openings are 

 on it, the female being in front of it ; the female openings are on it, and the 

 male behind it in Cryptodrilus, Perichaeta, Deinodrilus, etc. ; finally in the 

 Lumbricidae both orifices are in front of it. 



As a rule the clitellum is saddle-shaped, the glandular development 

 being confined to the dorsal and lateral regions, but in some forms it 

 is a complete girdle. Its secretion serves to make the cocoon, and in 

 some earthworms at any rate to bind the worms together in copulation. 

 Long modified setae are found in some forms in the neighbourhood 

 of the male pores, and protruding through them; and in a few 

 species bundles of similar setae are found near the spermathecae. 

 They are termed genital setae, those near the male pore being male 

 penial setae, and those near the spermatheca pore female copulatory 

 setae. When these modified setae are present, the ordinary setae of 

 the segment are absent. The cocoons in which the eggs are enclosed 

 may be spheroidal; more usually they are ellipsoidal, the two poles 

 being prolonged into short projections. They are formed by the 

 secretion of the clitellum which the worm slips over its head. As 

 the cocoon passes over the openings of the generative organs, it 

 receives the ova, spermatozoa, and albumen which form its ultimate 

 contents. Being elastic it shrinks when free of the worm and forms 

 a compact case, traces of its origin being generally retained in the 

 two projections from its poles. The cocoons are attached to aquatic 

 plants (Limicolae), or deposited in damp earth (Terricolae). It is 

 common, though not universal, to find that only one embryo in each 

 cocoon attains full development. There is no free larval stage : the 

 young leave the egg as minute fully formed worms. 



Earthworms copulate. In the common earthworm of this country the process 

 may be observed as follows : two worms in neighbouring burrows apply the 

 anterior ends of their bodies together (the posterior ends remaining in the 



