AS TO THE HBEEUITT OF ACaUIilED OONDITIONS. 499 



arrived at. These have been already sufficiently indicated in the 

 earlier sections of this paper, and need not, therefore, be now 

 further specified. Much more extended observations will be 

 required in most of these cases before it will be possible to settle 

 the question as to their nature. 



(4) There are certain malformations which suggest the possi- 

 bility that they may have been gradually acquired and subsequently 

 transmitted to descendants. Some of these may now be briefly 

 mentioned. The question of hereditary myopia and hypermetropia 

 is one which "Weismanu has considered in his essay " On Here- 

 dity "*. He there states : — " Those fluctuations on either side of 

 the average which we call hypermetropia and myopia, occur in 

 the same manner, aud are due to the same causes, as those which 

 operate in producing degeneration in the eyes of cave-dwelling 

 animals. If, therefore, we not unfrequently meet with families 

 in whicli myopia is hereditary, such results may be attributed to 

 the transmission of an accidental disposition on the part of the 

 germ, instead of to the transmission of acquired short-sightedness. 

 A very large proportion of short-sighted people do not owe their 

 affliction to inheritance at all, but have acquired it for themselves ; 

 for there is no doubt that a normal eye may be rendered myopic 

 in the course of a lifetime by continually looking at objects from 

 a very short distance, even when no hereditary predisposition 

 towards the disease can be shown to exist. Such a change would 

 of course appear more readily if there was also a corresponding 

 predisposition on the part of the eye. But I should not explain 

 this widely-spread predisposition towards myopia as due to the 

 transmission of acquired short-sightedness, but to the greater 

 variability of th.e eye, wh.ich necessarily results from the cessation 

 of the controlling influence of natural selection." I have already 

 mentioned that Mr. Priestley Smith has stated that there is a 

 supposed correlation between the growth of the brain and the 

 growth of the eye, by reason of which a high degree of cerebral 

 development is apt to be associated with an over-development of 

 the eye. If this be so, apparently the brain condition is the 

 primary factor, at least in a certain number of cases. But the 

 brain condition may be due to variations in the germ itself aud, 

 therefore, blastogenic in nature, and the inheritance of the defect 

 might follow without any necessity for an appeal to the heredity 



* EagUsh ed. (Ponlton). p. 89. 



85* 



