96 NATURE AND LIFE. 
confirms this. The slightest causes, the least deviations, 
whether spontaneous or occasioned, in the arrangement of 
the blastodermic or the embryonic cells, endanger the 
regular growth of the new individual, by inducing either 
the production of monstrosities or the death of the germ. 
When that is checked in its evolution, its natural envelopes 
continue theirs, and we find the growth of what is called 
a mole. In fact, the idea must be clearly fixed that the 
cells we have been speaking of have absolutely only a sin- 
gle function and a single power: that of providing the 
conditions required for the growth of the earliest organs 
of the embryo, namely, the dorsal and ventral layers. 
These layers are, in their turn, the starting-point for the 
dorsal cord, which ends in the appearance of the two halves 
of the central nerve-axis. Then come, after the vertebral 
cartilages, the eyes and auditory vesicles, the heart, the 
veins, the blood, etc. Every one of these organs becomes, 
on making its appearance, the cause of the generation of 
the next, so that, if any circumstance disturbs or puts an 
end to the production or the development of the former, 
the latter either does not show itself, or else comes out as 
a monstrosity. In the case of trout, salmon, and pike, 
seventy or eighty per cent. of the eggs, artificially fertilized, 
die. Lereboullet, to whom we are indebted for this inves- 
tigation, also points out that out of a hundred eggs hatched 
the number of monsters produced varies between two and 
five. The human being is subject to the same accidents. 
In three thousand births, there are always at least two 
hundred still-born in Paris and half as many in the rest of 
France, and among a hundred still-born an average is found 
of one monster not viable. Independently of the still-born, 
we find in the human race a number of congenital anoma- 
lies, which, though they do not threaten life, do often 
shorten it and make it difficult, by interfering with the 
regular exercise of its functions. Cretinism, idiocy, deaf- 
