regulating Metabolism . 5 1 7 
with Darwin’s conclusion that they are very active ; but the experiments 
were carried out in ordinary soft glass tubes and, suspecting that ammonia 
might be liberated, we were led to repeat them carefully in hard glass 
vessels. At room temperatures the chloride, nitrate, phosphate and sul- 
phate were practically without effect, although as the temperature was 
raised they became slightly active ; the ammonium salts of weak organic 
acids were more active. 
Although we are not yet prepared to grade ammonium salts in their 
order of activity, we are convinced that the salts of the strongest acids are 
the least active and that the activity is consequent on the liberation of 
ammonia by hydrolysis. 
Whatever explanation be given ultimately of Darwin’s observations, 
a sense of wonderment at the perfection of the inquiry must be felt by all 
who study the record in the light of modern knowledge. The stimulus 
that ‘ Insectivorous Plants ’ gave to the study of the process of digestion is 
probably far greater than is realized ; inspiration is still to be found in its 
pages ; indeed, not a few of the problems to which attention was called by 
Darwin now deserve reconsideration in detail. 
The information given by Loeb in the various accounts of his experi- 
ments on artificial parthenogensis in some respects supplements that to be 
derived from Darwin’s account of the behaviour of Drosera and from the 
behaviour of leaves such as that of Aucuba. The characteristic feature in 
the development of the sea-urchin egg by artificial means appears to be the 
formation of a ‘ fertilization membrane ’ at an early stage in consequence 
of an inflow of water which determines a growth in size of the egg. 
A similar effect may also be produced by placing the eggs in distilled 
water instead of in a solution of the hormone in sea-water or some similar 
liquid. If the action either of water or of hormone be allowed to continue, 
the cell breaks down entirely. 
One effect of the hormone on the leaf, as we have shown, is that it 
conditions the entry of water ; it is clear that this effect is also produced in 
the case of the sea-urchin egg. As the egg must be in equilibrium with the 
sea-water from which it is taken, it is to be expected that water would 
diffuse into it when distilled water is substituted ; what is surprising is that 
so much water should be absorbed as a consequence of the entry of the 
spermatozoon or the introduction of a minute proportion of some hormone. 
Ovum and spermatozoon are reciprocally affected as soon as the contact is 
effective. It is obvious that the spermatozoon is affected as it soon merges 
in the ovum ; and not only do changes become apparent within but also with- 
out the egg-cell — the superabundant spermatozoa in its neighbourhood 
being not merely warned off but even slain. Obviously, some hormone is 
produced which passes out rapidly into the medium surrounding the ovum. 
The effect produced by the spermatozoon apparently is never exces- 
M m 
