Chap. XXII. 



CAUSES OF VAEIABILITY. 



269 



The period of life at which the causes that induce variability act, is 

 another obscure subject, which has been discussed by various authors. 49 In 

 some of the cases, to be given in the following chapter, of modifications from 

 the direct action of changed conditions, which are inherited, there can be no 

 doubt that the causes have acted on the mature or nearly mature animal. 

 On the other hand, monstrosities, which cannot be distinctly separated 

 from lesser variations, are often caused by the embryo being injured whilst 

 in the mother's womb or in the egg. Thus I. Geoffroy St. Hilaire 50 asserts 

 that poor women who work hard during their pregnancy, and the mothers 

 of illegitimate children troubled in their minds and forced to conceal their 

 state, are far more liable to give birth to monsters than women in easy 

 circumstances. The eggs of the fowl when placed upright or otherwise 

 treated unnaturally frequently produce monstrous chickens. It would, 

 however, appear that complex monstrosities are induced more frequently 

 during a rather late than during a very early period of embryonic life ; 

 but this may partly result from some one part, which has been injured 

 during an early period, affecting by its abnormal growth other parts subse- 

 quently developed; and this would be less likely to occur with parts 

 injured at a later period. 51 When any part or organ becomes monstrous 

 through abortion, a rudiment is generally left, and this likewise indicates 

 that its development had already commenced. 



Insects sometimes have their antennas or legs in a monstrous condition, 

 and yet the larvas from which they are metamorphosed do not possess 

 either antennas or legs; and in these cases, as Quatrefages 52 believes, we 

 are enabled to see the precise period at which the normal progress of deve- 

 lopment has been troubled. But the nature of the food given to a caterpillar 

 sometimes affects the colours of the moth, without the caterpillar itself 

 being affected; therefore it seems possible that other characters in the 

 mature insect might be indirectly modified through the larvas. There is 

 no reason to suppose that organs which have been rendered monstrous 

 have always been acted on during their development ; the cause may have 

 acted on the organisation at a much earlier stage. It is even probable that 

 either the male or female sexual elements, or both, before their union may 

 be affected in such a manner as to lead to modifications in organs de- 

 veloped at a late period of life; in nearly the same manner as a child may 

 inherit from his father a disease which does not appear until old age 



In accordance with the facts above given, which prove that in many 

 cases a close relation exists between variability and the sterility following 

 from changed conditions, we may conclude that the exciting cause often 

 acts at the earliest possible period, namely, on the sexual elements, before 

 impregnation has taken place. That an affection of the female sexual 

 element may induce variability we may likewise infer as probable from the 

 occurrence of bud-variations ; for a bud seems to be the analogue of an ovule. 

 But the male element 1S apparently much oftener affected by changed con- 



49 Dr. P. Lucas has given a history 

 of opinion on this subjeet : ' Hered. Nat ' 

 1847, torn. i. p. 175. 



a0 ' Hist, des Anomalies/ tom.iii.p.499. 



51 Idem, torn. iii. pp. 392, 502. 



52 See his interesting work, 'Meta- 

 morphoses de rHomme,' &c, 1862, p. 

 129. 



