206 Heredity. 



lesion so slight that the microscope can scarce detect it, gives rise 

 to mental disorganizations called delirium, insanity, monomania. 

 In short, we may lay it down as a general truth, solidly based on 

 experience, that the more complicated the mechanism, the greater 

 the disproportion between accidental causes and their effects. 



The study of anomalies, and the artificial production of mon- 

 strosities, afford us convincing proofs of this truth. The researches 

 of Geoffroy Saint-Hilaire and of Dareste have shown that it is 

 possible to produce monsters at will, and that these deviations 

 from the type are brought about by trifling causes. Hens' eggs 

 when set on end, or in any way disarranged, produce monstrous 

 chickens. And the same thing occurs if the eggs be shaken, or 

 perforated, or partially coated with varnish. Isidore Geoffroy 

 Saint-Hilaire shows that women of the poorer class who are 

 obliged to work hard during pregnancy, as also unmarried women 

 who are forced to conceal their pregnancy, far more frequently 

 than other women give birth to monsters. ' Certain monstrosities/ 

 he writes, 'are often caused by lesions which happen to the 

 embryo in the uterus or in the ovum. Yet it would seem that 

 complex monstrosities are more often determined at a later period 

 than at the beginning of embryonic life. This may in part result 

 from the fact that a point which suffered injury in the origin of the 

 phenomenon, afterwards by its anomalous growth, affects the other 

 points of the organism which have afterwards to be developed.' 

 His Hisloire des Anomalies, to which we would refer the 

 reader, is full of curious facts, well fitted to stimulate thought. 

 It will be seen that insignificant causes are sufficient to effect 

 either a fusion of homologous parts, or inequalities of develop- 

 ment checks to growth ' which make anomalous beings, in some 

 respects, permanent embryos, in which nature has halted half-way.' 



In presence of such facts, it is not possible to accept futile 

 explanations which have only an appearance of simplicity : for 

 instance, ' As is the effect, so is the cause ; there must exist in the 

 cause at least as much as in the effect.' Such explanations are 

 available only in very simple cases, or at best in complicated cases 

 of a purely mechanical kind. According to a profound remark of 

 John Stuart Mill, whenever an effect is the result of sundry causes 

 (and nothing is more frequent in nature), we can have two cases : 



