THE EARTHWORM 35 



and opens to the exterior by the spermiducal pore on segment 

 15. The duct of each member of the second pair of ciliated 

 rosettes passes through the septum dividing somites n and 12, 

 and after a short convoluted course joins the duct of the 

 anterior rosette in segment 12. It should be clearly under- 

 stood that the median seminal reservoirs lie below the 

 oesophagus, but cover in the testes, the ciliated rosettes, and 

 the ventral nerve cord (fig. 4, JB). 



In each of the somites 9 and 10 there is a pair of accessory 

 organs in the shape of small white spherical vesicles, opening 

 by small intersegmental pores between segments 9 and 10 

 and 10 and n. These are the spermathecse, and at certain 

 times of the year they contain large numbers of ripe sper- 

 matozoa; long filiform bodies slightly thickened at one end, 

 and capable of active movement. The spermatozoa are formed 

 in the sperm-sacs and seminal reservoirs from the sperm 

 mother-cells derived from the testes. The sperm mother-cells 

 divide in such a way as to form a peripheral layer of cells 

 attached by their inner ends to a central generally non- 

 nucleated mass of cytoplasm called the cytophore. The 

 nucleated cells surrounding it gradually increase in length, 

 and eventually are drawn out into long filiform structures 

 adhering by their thickened inner ends to the cytophore. 

 Ultimately they are detached as ripe spermatozoa, and are 

 drawn by the cilia of the rosettes into the sperm-ducts, through 

 which they pass to the exterior. From the sperm-ducts the 

 spermatozoa are transferred to the spermathecse of another 

 worm, two worms in adjoining burrows coming together for 

 this purpose. 



The ova of the earthworms are laid in cocoons which are 

 formed by the secretion of the glands of the clitellum. The 

 secretion hardens on exposure to the air, forming a mem- 

 branous ring which the worm slips over its head. As the ring 

 passes the openings of the oviducts and spermathecaa it 

 receives a number of ova and spermatozoa, and also albu- 

 minous matter secreted by certain capsulogenous glands 

 situated on the ventral side of some of the segments anterior 

 to the clitellum. As the cocoon is elastic, it shrinks when 

 free of the worm, the middle part is swelled out by the ova 

 and albumen and the two ends are reduced to tag-like 

 projections. The cocoons are deposited in the earth. As a 



