18 EARTHWORMS AND LEECHES [CH. I 



the so-called capsulogenous glands, which may be seen on 

 the ventral side of some of the segments in front of the 

 clitellum. The cocoons, at first white but soon becoming 

 yellow, are left in the earth, and as a rule only one of the 

 contained eggs produces a young worm. The size of the 

 cocoons differs in the various species, those of L. terrestris 

 are from 6 to 8 mm. long by 4 to 6 mm. broad, of Eisenia 

 foetida from 4 to 6 mm. long by 2 to 3 mm. broad. There 

 is some doubt as to the precise function of the sperma- 

 thecse. It seems certain that the spermatozoa contained 

 in them are derived from some other worm. It is also the 

 case that these organs are full of spermatozoa prior to 

 sexual union, and are empty subsequent to that act, at 

 any rate when cocoons are formed and eggs deposited. 

 Worms have been observed to separate without producing 

 cocoons, and though perhaps in some instances the sepa- 

 ration may have been due to disturbance caused by obser- 

 vation, yet there is reason to think that two unions are 

 necessary, one to fill the spermathecse, and a second to 

 form cocoons. In such a case it is probable that each 

 worm acts as a carrier of spermatozoa from its first to its 

 second mate, i.e. worm A gets its spermathecaB filled by 

 the spermatozoa of B in the first union, and passes these 

 spermatozoa to C in the second. The actions are probably 

 often reciprocal. According to Goehlich 1 while sperma- 

 tozoa are flowing from one worm to the spermathecse of 



1 Semper's Zool. Beitr. n. ; cf. also Wilson, Journ. Morph. iv. ; K. 

 Foot, Journ. Morph. xiv. 1898, and Zool. Bull. n. ; Hering, Zeit. wiss. Zool. 

 viii.; Bergh, Zeit. tviss. Zool. XLIV and L. 1890; Kosa, Bull. Mus. Zool. 

 Anat. Torino, iv. ; Vejdovsky, Entwick. Untersuch. Prag. 1888 1892; 

 Britscher, Biol. Centralbl. xxi. 1901. 



