ASPECTS
ANI) ETIOLOGY OF CARCINOMA 57
of
this from the organism, its conversion into a primitive germ-cell, and the
consequent formation of primary germ-cells from this. Normally, as already
stated, the further development of a primary germ-cell results in an embryo,
not in a larva (asexual generation).
Coming
now to the primary germ-cells, upon which many observations have been made, it
has elsewhere been established that their number is always a member of the
geometrical series 2, 4, 8, 16, 32, etc., or 2 to the nth
power, where n is one of the numerals 1, 2, 3, 4, 5, 6,
etc., and that the greatest number of primary germ-cells in any embryo will be
2n- 1. Thus, the total number in the common dog-fish (Scyllium
canicula) is 128; in the male smooth skate (Reja batis), 256 ; in
the female, 512 ; and the greatest number in the embryo of one of these 127 (in
Scyllium), 255 (in the male skate), and 511 (in the female
skate). But for convenience and brevity, dealing with one form only—say, the
dog-fish (Pristiurus)—of the 127 primary germ-cells, it never
happens that all, or anything like all, reach the normal position—the germinal
ridge or nidus. Usually, at the most from 90 to 100 of them
arrive here, the remainder being found in all sorts of unusual places, where
many of them degenerate.
Here
may be inserted a very brief account of some unpublished finds, which for this
reason have escaped the attentions of some observers intent upon “ annexation.”
Some ten years ago my observations proved to me that in certain dog-fishes (Scyllium
and Pristiurus) the single ovary of the adult female arose by the
degeneration during development of the left embryonic ovary and the persistence
of the right one. There were at the time many indications—even strong
evidences—that the find in the female skate of twice as many primary germ-cells
as in the male was a general rule for the back-boned