TUBIFEX. 351 



and having the form of a voluminous gland, greyish in 

 colour. What he has described as the testis is really a 

 portion of the sperm sac, for the latter in a mature worm 

 not only extends backwards through several segments, 

 but may pass forwards in front of that segment which 

 originally contained the testis. Mcintosh (1871), too, 

 has confused the sperm sac with the testis in stating that 

 the testis of one side remains in segment 9, while its 

 fellow extends back as far as segment 16. 



The ovaries are still small when the testes have 

 attained their full size, but while the latter soon disappear 

 the ovaries gradually increase in size until they occupy a 

 large proportion of segment 11. In a fully developed 

 ovary it is easy to recognise ova in several stages of 

 development. 



II. Development and Structure of the Spermatozoa. 



The germinal epithelium in the testis gives rise by 

 ordinary cell division to a number of spermatogonia, 

 which, at an early stage in their development, are 

 separated from the testis and pass into the sperm sac, 

 which, at first, is a simple, undivided sac. The spermato- 

 gonia, when they leave the testis, are uninucleate, but 

 very soon the nucleus divides several times, and, as its 

 division is not at once accompanied by division of the 

 cytoplasm, each spermatogonium or sperm morula, as it 

 is called, becomes multinucleate (PI. V, figs. 28 and 29). 

 (id kins (1895a), who has described in detail the 

 spermatogenesis of Lumbricus, states that the spermato- 

 gonia, while still in the testis, are multinucleate. 

 Careful examination of many preparations of the 

 spermatogonia of Tubifex has led me to decide that in 

 this form, at any rate, the spermatogonia only become 

 multinucleate on leaving the testis, 

 x 



