134 E. W. MvVOBRIDE. 



effectively, there is no control over the orientation, and it is 

 impossible to get thin enough sections. I found it necessary 

 to use for my youngest and most important stages sections 

 3J H thick (five teeth of the rocking microtome). Above a 

 diameter of '3 mm. my sections were 4^ fx thick (seven teeth), 

 and only for adults and the oldest stages did I use sections 7 fi 

 thick (ten teeth). 



Sections perpendicular to the disc, but transverse to the axis 

 of the stone canal, and horizontal sections were also used, but 

 proved to be not nearly so instructive as those orientated as 

 described above ; they were useful, however, in determining 

 some minor points. 



My results are founded on perfect series of sections with 

 finely differentiated stain and clear, sharp outlines. The sec- 

 tions themselves are clearer and more diagrammatic than the 

 figures I have been able to make of them. In fact, I obtained 

 preparations which for distinctness of outline and diagrammatic 

 alternation of colour could hardly, I think, be surpassed by 

 the use of osmic acid, Miiller's fluid, paracarmine, and hseraatin. 



It will be most convenient to first of all detail my results, 

 and then to examine and discuss the literature; and as the 

 ovoid gland precedes in development the genital organs, it will 

 be well to commence with it. 



Ovoid Gland. 

 I. Structure. — This has been described by Cuenot (4), 

 Hamann (7), Apostolides (1), Ludwig (11), and Kohler (9). 

 They agree in describing a pyriform mass enclosed in a space 

 limited by a strong membrane, and almost filling it. Most 

 agree in finding a supporting network of fibres with meshes 

 partly occupied by cells, partly forming lacunae. This mass 

 sends out a prolongation, gradually becoming like ordinary 

 connective tissue, towards the nerve-ring. On the dorsal sur- 

 face of the latter it enters into connection with a structure 

 called the ha3mal ring. At its lower end the gland is pro- 

 longed into a curious string of tissue enclosed in a prolonga- 

 tion of the sinus which surrounds the gland. This string (the 



