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injury has altogether altered the ornamentation of the shell. 
Such injury has invariably caused reversion—the ornaments of 
a fairly remote ancestor appear in consequence of the injury ; 
and this has led me to say in my Monograph that Atavism is a 
consequence of diminished vitality, whether such enfeeblement 
is due to old age or to injury. But so far as the inheritance 
of variations due to injury is concerned I have not yet noticed 
anything of the kind. 
Of variations due to disease—the word being used in a 
wide sense to include the effects of any suddenly unfavourable 
conditions of life—-Ammonites furnish several examples ; 
although it is not always easy to distinguish between the effects 
of disease and long-continued retrogression. In the latter, 
however, there are definite stages to be passed through; but 
if some of these stages be omitted and the Ammonite shews 
any abnormal features it may be considered as influenced by 
suddenly unfavourable surroundings. Oecotyptius refractus ap- 
pears to be an instance of variation due to disease being 
inherited.* Concerning Occotraustes cadomensis (d’Orbigny) I 
am not so certain; because to produce this form retrogression 
had proceeded regularly, and the abnormal whorl-shape may 
only be the further continuation thereof. The lopsided Ammon- 
ites of the Lias, which d’Orbigny called Turrilites, are certainly 
variants due to disease or unfavourable conditions; but whether 
this peculiarity was inherited, or whether it was simply the 
[*I extracted the following from the 50th Report (1891) Bristol Distr. 
Institution for Deaf and Dumb, p. 14, Bristol, 1892, (kindly sent by Mr Lucy.) 
It is of interest in connection witk Abnormal Variation and its inheritance. 
“From cases investigated it was found that there were 46 children born 
whose parents were pupils at the Institution, and none of those suffered from 
the physical infirmities of their fathers or mothers. There were 12 instances of 
deaf and dumb couples, 13 where the husband only was deaf and two where the 
wife was deaf and dumb. Out of 138 cases enquired into of pupils received at 
the school it was discovered that with one exception their parents were not 
similarly afflicted. The causes of this sad affliction are various, but 60 % are born 
deaf and dumb. Variation I.,1,p. 263. And the next most prolific cause is 
scarlet fever.” Variation I., 2, p. 264. ] 
