Ill 
1888-89.] Mr J. A. Thomson on Theory of Heredity. 
( 2 ) Apart from the general connectedness and the common 
medium of the blood, it seems worth while to refer to the 
frequent occurrence of protoplasmic continuity within the 
system. In plants the intracellular connections by means of 
protoplasmic bridges are widespread ; this is true in a more 
limited degree of animals. How open in such cases is the 
organism to an influence from the body to the reproductive 
cells 1 Take such a case, not altogether unique, as the 
embryo Peripatus , where, according to Sedgwick, an actual 
syncytium of cells obtains for a considerable time, how 
difficult it is there to conceive of the keimplasma keeping 
quite intact, in spite of somatic influences which may play 
upon it. 
( 3 ) Even in the comparatively few cases where a continuity of repro- 
ductive cells is demonstrable, it does not seem justifiable to re- 
ject the notion that these may be affected by the somatic sheath 
which has grown up around them. They are surely reachable 
by the anastates and katastates of the body, which is simply 
a more exact way of expressing the penetration of “ scent- 
stuff” which Jager maintained, or the limited liberation of 
gemmules which Galton allowed. But in most cases, as we 
have seen, there is not even a continuity of reproductive 
cells, but only a continuity of a specific reproductive proto- 
plasm or nuclear plasma. How much more difficult, then, is 
it to conceive of this as remaining practically untouched by 
the physico-chemical conditions of the “ soma ” 1 Even 
Weismann at times admits that nutritive vacillations may 
produce “ ever so little modifications in the molecular struc- 
ture of the keimplasma.” Proof of the degree of modifica- 
tion possible may be as legitimately demanded on the one 
side as on the other. A continuance of many “ ever so 
littles ” may amount to much. Hor is it possible to draw 
any hard line between modification of the germ-plasma along 
with and through the general “body.” 
( 4 ) It is useful, also, to allude to the numerous experiments 
which have been made on the determination of sex. Take 
only one example, the familiar case of Yung’s tadpoles, 
where, by altering the quantity and quality of the food, he 
