TUBIFEX. 383 



various parts will be well differentiated, the heads of the 

 spermatozoa staining well with the borax-carmine, and 

 the tails with the picro-indigo-carmine. 



The spermatophores are visible to the naked eye, and 

 when first liberated from the spermatheca appear as 

 small, fine, white, glistening bodies, the largest being 

 about 1-2 mm. long. When examined under the 

 microscope they will be seen to have quite a complicated 

 structure, but before describing this it will be well, 

 perhaps, to say a word or two about their formation. 

 During copulation, the spermatozoa, together with the 

 secretion of the gland cells of the prostate, are transferred 

 from one worm to the spermathecae of the other. It seems 

 certain that the moulding, which must take place before 

 the spermatophores attain their final shape, is carried out 

 entirely in the spermatheca, and moreover in one part 

 only of the spermatheca, viz., its duct. The duct leading 

 from the external aperture to the pouch is so narrow, and 

 the quantity of sperm forced in so great, that the mass 

 must necessarily conform very closely to the shape of the 

 duct. And this we find is the case even to the minutest 

 detail. We will first describe the general form and 

 minute structure of the spermatophore, and then show 

 how this agrees with the general shape of the sperma- 

 thecal duct. 



The fully-formed spermatophore is a narrow, much 

 elongated structure, many times longer than broad, and 

 somewhat worm-like, its widest part being near the 

 middle and tapering off at both ends. The anterior end is 

 always simple in structure, but the posterior end may be 

 similar to it or may terminate in a beautifully moulded 

 and curved conical head (PI. VII, fig. 50). It has been 

 suggested that the presence or absence of a conical head 

 is characteristic of two different species, but this is 

 z 



