58 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
the cytocyst may be compared to the blastula, so far as the relation 
of the cells to the enclosed cavity is concerned. The causes for the 
hollow condition may be the same in both cases. Loeb has attempted 
a physical explanation of the hollow condition of the blastula, by 
assuming that the cells acquire a peculiar affinity for water, and hence 
favor its accumulation in the form of a large water vacuole in the 
center. Such an explanation is probably altogether inadequate. In 
the living material of teased testis, it appears more like an electrical 
phenomenon, the similar spermatocysts having been previously, as 
secondary spermatogones, crowded together as if attracted to one 
another, now, as division ceases and growth begins, being suddenly 
repelled from each other, and attracted by the unlike cyst cells. 
Mutual repulsion on the part of the spermatocysts, and attraction 
between them and the dissimilar cyst cells would, of course, produce 
the hollow vesicle. The suggestion may perhaps be pardoned, purely 
theoretical as it is, that during karyokinesis, the opposite poles of each 
spermatogone are differently charged electrically; hence the mutual 
attraction of the cells at the spermatogone stages; while during the 
growth period the entire cell is similarly charged, hence the repulsion 
between them. Such repulsion may, for aught we know, favor the 
expansion of the cell, and hence be one of the leading factors in absorp¬ 
tion and nutrition. This hypothesis of an electrical charge is partly 
sustained by the singular movements already described at the close 
of the introduction to this paper as being one inciting cause of my 
undertaking this study. 
When the spermatocytes enter on their maturation divisions, the 
cytocyst is often very large (pi. 13, fig. 35-39). The size, however, 
varies. In the same testis, and on the same slide, but usually in dif¬ 
ferent follicles there are cytocysts varying greatly in size while the 
contained spermatocytes are in the same phases of maturation. In 
the large cysts the cells are correspondingly large. They give rise to 
giant spermatids (pi. 13, figs. 36, 39; pi. 14, fig. 46; pi. 17, fig. 138). 
Spermatocysts. 
Soon after maturation, the spermatids begin to elongate and the 
spermatocysts lose their spherical form. At one pole the cyst cells are 
crowded out, and the cyst becomes oval or ovate in outline (pi. 12, 
fig. 14). From this stage on, the cyst elongates, finally becoming 
