68 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
This constant pinching off of the primary spermatogones in this 
way accounts for their accumulation here in the neighborhood of the 
grandmother stem cell, and for their absence in all other parts of the 
testes. It explains, too, how the production of new spermatozoa is 
possible in the adult butterfly even though all gonocysts are already 
well developed in the very young larva. 
Summary on the grandmother stem cell .— I am not aware that an 
account has ever been published of a similar case, and I consequently 
anticipate on the part of my readers a scepticism no less hostile than 
has been my own during my study of this subject. I therefore sum¬ 
marize the facts on which my conclusions are based: — 
«/ 
1. There is at least one, but may be as many as four grandmother 
stem cells in a testis (pi. 12, fig. 8b). 
2. There are no free spermatogones except in the immediate 
vicinity of this cell (pi. 12, fig. 4). 
3. Follicles that do not contain such a cell, soon have all their 
contents converted into mature spermatocysts (pi. 12, fig. 5, /.). 
4. Follicles containing this cell continue to function to the end 
of the breeding season (pi. 12, fig. 5, g. c., g.m. s.). 
5. The cell exists in the immature testis of the young larva (pi. 
15, fig. 56) as well as in that of the adult near the end of the breeding 
season (pi. 12, fig. 5). 
6. The body of the cell though very large is apparently undiffer¬ 
entiated resembling arehoplasm in its homogeneity (pi. 12, fig. 4). 
7. The nucleus sometimes shows signs of amitotic division (pi. 
15, fig. 57a). 
8. The cell is amoeboid in outline, sending out protoplasmic 
strands all over its spherical surface (pi. 15, fig. 56). 
9. Apparently imbedded in its peripheral protoplasm are numerous 
minute nuclei, cortical nuclei, which because of their variable size 
and shape are easily mistaken for granules surrounding the central 
cell (pi. 12, fig. 4). 
10. Attached to the end of each protoplasmic process or branch 
is a conical cell (mother branch cell), with its apex turning inward 
toward the central grandmother cell (pi. 12, fig. 4). 
11. The conical branch cell divides independently of other cells 
by mitosis (pi. 12, fig. 4). 
12. The position of the spindle is invariably in the long axis of 
the cell, the spindle axis being in line with the protoplasmic branch 
