at different Degrees of Constant Temperature. 263 
We may infer, from the demonstrated existence of a mini- 
mum, that a mean temperature does not produce the same 
effect as the same constant temperature, unless, perhaps, the 
question is that of a mean calculated above the minimum 
requisite for the species and below the degree at which the heat 
becomes injurious to it. On deducting the useless and unfavour- 
able degrees, the means may possibly act as a similar constant 
temperature. I see, however, a reason for doubting this. It 
is that temperatures which are too low for the germination of a 
species, are probably not so as far as relates to some particular 
detail of the function of germination. Low temperatures ap- 
peared to me injurious to the absorption of water by the surface 
of the seeds; however, slight absorption might occur, which 
would be beneficial subsequently when the temperature rises for 
a time. The same holds good in the case of other internal 
phenomena of the seed. Hach of them is a function in the 
general evolution of the germination, and each has its minimum 
and maximum. Nothing in nature is simple, even in that which 
appears comparatively very simple. 
9. Analogy between seeds and eggs. 
Some naturalists have ventured to affirm the existence of 
a kind of identity between a seed and an egg. There is, how- 
ever, in a physiological point of view, this great difference, that 
the embryo is almost entirely stationary and inert in the interior 
of the seed, while atmospheric influences act upon the -animal 
contained in the egg, and must act to prevent the animal from 
perishng. The egg constantly disengages carbonic acid and 
aqueous vapour. It therefore requires air, while the seed can 
dispense with it. 
However, to all the existing points of resemblance, it must 
be added that zoologists are at present content, like botanists, 
with rather vague notions of the effects of temperature upon the 
germs. If I have been well informed, and I have consulted 
good authorities, exact and slightly varied experiments upon in- 
cubation at definite thermometric degrees have not been made, 
There is, however, a memoir upon rearing silkworms, by MM. 
Millet and Robinet and Madame Millet, which contains precise 
details upon one species. These authors say that, “to hatch silk- 
worms, the eggs must be subjected to a temperature of +9° C. 
The number of degrees necessary for incubation diminishes at 
the same time as the number of days employed in producing them. 
In other words, if it is required to distribute the number of degrees 
of heat between fifty days on the one hand and one hundred on 
the other, this number is found to be more than sufficient in the 
first case, and the hatching takes place before the employment 
