70 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
third, a dividing spermatogone; fourth, a gonocyst in the two-celled 
stage; fifth, a gonocyst in the four-celled stage; sixth, a gonocyst in 
the eight-celled stage, sixteen, thirty-two, etc., stages. 
25. The grandmother stem cell group is always found close to 
the inner pigmented layer, at the periphery of the follicle (pi. 12, fig. 
4, g), never in the center of a follicle nor near the vas deferens where 
the mature spermatozoa and the stalked cells are found (pi. 12, fig. 5). 
When all the above facts are considered together, it will be conceded 
that my conclusion in regard to the character and function of the 
grandmother stem cell is fully justified. The subject certainly deserves 
further study in other forms. As I find this cell also in a different 
genus of butterfly, Grapta silenus, I am surprised to find no mention 
of it by Henking (’ 92 ), Paulmier (’ 98 ), or Wilcox (’ 95 ) in their work 
on other insects. Paulmier claims to have studied Papilio, and 
draws one of his most important conclusions concerning the centro- 
some from it. 
A suggestion .— In my “Researches on the oogenesis of Clemmys 
marmorata ” (’ 04 ) I found that the follicle cells are the sister cells of 
the egg, having originated from the same primordial oogonium. 
The relation of the mother branch cells to the grandmother stem cell 
resembles very much the relation of follicle cells to the egg. This, 
I have already pointed out, is suggested when we examine an ovary 
of the butterfly larva. Without running the risk of drawing unwar¬ 
ranted conclusions, it may be suggested, at least, that we seem to have 
in this grandmother stem cell a singular reversal of function. In the 
female the central cell functions as the germ cell, while in the male, 
the peripheral cells corresponding to the follicle cells of the ovary 
become.the germ. If there is any homology between this grandmother 
stem cell and the Sertoli cell of the mammalian testes, then may not 
the Sertoli cell be homologous with the ovum of the mammalian 
ovarv ? 
•/ 
History of the Spermatogonia. 
In the preceding account of the grandmother stem cell, I have given 
the evidence for my conclusion that the primary spermatogones orig¬ 
inate from the mother branch cell by division of the latter (pi. 15, 
fig. 57, /). The distal half becomes a free primary spermatogone, 
