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- 



