1874.] 239 {Hyatt. 



ance of the primary or ancestral form and characteristics of the 

 series is due to the encroachments of the inherited old age character- 

 istics. When these, which are essentially degradational, begin to be 

 inherited in a race, the adult characteristics begin to be confined to 

 younger periods of growth and finally disappear altogether, the shell 

 showing certain old age or inherited senile characteristics from the 

 beginning of the fourth stage. Everywhere this mode of inheritance 

 by acceleration occurs, everywhere it seems to govern ^ie succession 

 of the forms. I have not, however, been able yet to trace the precise 

 connection between all the roots of the secondary series. If this 

 could be completely done, which I fear is impossible at present, no 

 doubt some similar relations would be found. 



Besides those parallel forms which may be called progressive, there 

 are others in the same groups which may be shown to be due to the 

 inheritance of the old age of these same parallel forms, and, by com- 

 parison with similar forms prematurely produced in the different spe- 

 cies by disease or local influences, they may be attributed to similar 

 causes, namely, the action of unfavorable surroundings. It is no ex- 

 aggeration to say that in many instances the small, dwarfed forms 

 produced by disease are very similar to the normal and large old age 

 forms of the same series. This resembl ance extends sometimes even 

 to the mode of development. Disease thus produces directly an ef- 

 fect similar to the normal action of the laws of inheritance through 

 a greater or less period of time under the influence of physical sur- 

 roundings. 



The word surroundings is now used instead of environment, for the 

 reason that environment covers the whole ground of physical causes 

 which may have either a remote or immediate effect upon the life of 

 the species. 



The environment, or the sum of the physical influences, however 

 favorable it may seem to be, is, as is well known to all physiolo- 

 gists, perpetually inimical to the prolonged existence of life, and 

 brings about in the individual the retrograde metamorphoses known 

 as old age, and leads to death by the disuse, atrophy and decay of 

 the functions and organs. 



These changes in the individual are in precise correspondence 

 with those taking place in a group, and, as has been shown, these 

 characteristics are acted upon in their transmission from individual to 

 individual, during the decline of the group, by the same law of inheri- 

 tance as are the progressive characteristics during its rise. Thus it 



