606 W. R. Coe — Anatomy of Cerehratidus lacteus. 



substance of the ovum is largely made up of line yolk-granules. The 

 transparent germinal vesicle is about one-third the diameter of the 

 ovum, and often contains a highly refractive germinal spot one-third 

 as large as the vesicle itself. 



Spermatozoa develop from cells similar to those which form the 

 ova. In a section through a spermary (^Plate XIV, fig. 6) in which 

 the spermatozoa are developing rapidly we see, next the connective 

 tissue framework of the sac, several rows of cells in which are very 

 large nuclei (sc), and in which the cell-outlines are not readily made 

 out. Above these are several irregular rows of cells with much smaller 

 nuclei {sc). In the next stage we find still smaller, oval or elongate, 

 bodies which usually show a nucleus at one end while the rest of the cell 

 is filled with a clear protoplasm. These are, apparently, the developing 

 spermatozoa, although I was unable to trace the whole course of 

 development. These are followed by nearly ripe spermatozoa {sp) 

 which completely fill the lumen of the sac. The mature spermatozoa 

 (fig. 7) are long and slender, with a head-piece measuring about 

 .012'°™ in length. This head-piece is tapered to an exceedingly fine 

 point in front, while the opposite end is swollen into a bright globule, 

 from which goes off a tail-piece fully three times as long as the 

 head-piece. 



The writer wishes to express his gratitude for valuable criticism 

 and advice, both to Professor A. E. Verrill, at whose suggestion and 

 under whose direction this paper has been written, and to Professor 

 S. I. Smith, in whose laboratory the work has been done. 



