W. F. R. Weldon 
367 
first cases mentioned is that of certain wheat. The race to which this wheat 
belonged originated in temperate Europe, but by selection among plants grown in 
Norway, near the northern limit of possible culture, a form was produced which 
ripened earlier, and had heavier seeds than the parent form. Seeds from this 
form, when sown in more southern countries, gave rise after a few generations to 
plants which resembled the parent race. Here we have obviously to consider not 
only the cessation of selection, but the change in external conditions, as affecting 
the result. Again Professor de Vries himself shows that the number of super- 
numerary carpels in the fruit of Fapaver somnfferum pohjcepJialum, produced by 
plants grown from seed of the same parental fruit, varies enormously (from 150 to 
one or two!) according to the amount of nutrition supplied during particular stages 
of growth ; he says deliberately that the selection of plants with the greatest 
number of carpels is simply the selection of the best nourished individuals ; and 
yet the reduction in the number of extra cai'pels after cessation of selection is 
quoted as proof that the results of selecting mere variations are unstable. 
Now it cannot be too strongly insisted upon that every character of an animal 
or of a plant, as we see it, depends upon two sets of conditions ; one a set of 
structural or other conditions inherited by the organism from its ancestors, the 
other a set of environmental conditions. There is probably no race of plants or of 
animals which cannot be directly modified, during the life of a single generation, 
by a suitable change in some group of environmental conditions. 
The work of Dareste, Driesch, Herbst, and others has shown that some of the 
most normal and universal phenomena of animal development are each diiectly 
dependent for their occurrence upon a certain group of external conditions. 
Referring to the recent work of Herbst* for a valuable and suggestive summary of 
work already done, I take this opportunity of illustrating the connection between 
normal development and environmental conditions b}' a new example. It is well 
known that a hen's egg, at the normal temperature of incubation, loses roughly 
half a gram of water per day, by evaporation through the shell ; as a result of this 
the density of the medium by which the embryo is surrounded increases, and the 
bulk of this medium is so diminished as to produce the air space at the broad end 
of the egg. Some years ago I attempted to replace the water lost by evaporation 
without preventing the process of evaporation itselff. A hole was made in the 
broad end of the egg-shell and the subjacent membranes, into which one end of a 
siphon, filled with water, was fitted. The other end of the siphon was placed in a 
reservoir of water, and the whole apparatus placed in an incubator. In from 20 to 
30 per cent, of embryos treated in this way the amnion was largely or entirely 
absent after incubation for three or four days. In Fig. 1 (Plate III.) I have drawn 
an embryo, observed after 72 hours of incubation, and it will be seen that this 
embryo projects into the albumen without a trace of amniotic covering, like the 
embryo of a shark.- In Fig. 2 a more usual condition is represented. The embryo 
* Curt Herbst: Formative Reize in der thierischen Ontogeiiese, 8vo. Leipzig, 1901. 
t Preyer has shown that an egg, incubated in an atmosphere saturated with water, cannot develope. 
