486 SUMMARY OF CURRENT RESEARCHES RELATING TO 



enormously increased, the period from the birth of the parent to the 

 birth of the young being fourteen days at 16^ and six days at 30^ The 

 number of young per brood was diminished. The important results of 

 the experiment were the following. The specimens developed from eggs 

 laid by parents a few hours after removal from the higher to the lower 

 temperature were almost as small as those born at the higher temperature. 

 The subsequent eggs laid by the same parents, still under control con- 

 ditions, still remained affected by the smallness-producing conditions, 

 though to a rapidly diminishing extent. 



In a third set of experiments a reduction of length was caused by 

 living in Klebs' solution. The reduction was found to persist for a 

 short time, and was followed by a reaction. 



The experiments illustrate " parallel induction." In the first and 

 second sets of experiments, at any rate, individuals placed in abnormal 

 environments in their first instar acquired the definite abnormal features 

 in their own somas in later instars. Simultaneously, the eggs in their 

 ovaries were influenced in such a way that the young developed from 

 them presented at birth the same abnormality as that which their parents 

 had acquired in their lifetime. It made little difference whether the 

 young developed from eggs laid after removal of the parents to control 

 conditions, or were born in the abnormal environment, so long as the 

 eggs underwent their ovarian growth while the parents were under the 

 influence of the environment. In the subsequent broods of those parents 

 which had been removed to control conditions the effect of the abnormal 

 conditions appeared in rapidly diminishing intensity. In the next gene- 

 ration in control conditions (F2) the abnormal effect still persisted (in 

 the first two sets of experiments), but to a very slight degree. In all 

 three sets of experiments a very decided reaction appeared in F3. 



Mutations, giving rise to new genotypes, are due to a change in the 

 composition in the hving unit. " The other cause of variation — a 

 change in the environment while the living units remain the same — is 

 probably far commoner. Such a change, if effective, will probably result 

 in the formation of unusual metabolic products included in the living 

 protoplasm, and thus the visible external variation produced may have 

 as its immediate cause either the changed environment itself, or the 

 altered protoplasmic inclusions. In the case of parallel induction, it 

 seems that the environment works indirectly, through the mediation of 

 these (not living) products, which when once formed are not immedi- 

 ately got rid of, but are passed on passively included in the protoplasm 

 of the gamete." Some (not living) product is included in the egg, passes 

 passively into the soma which develops from the egg, and thus pro- 

 duces on the soma the same effect as it produced on the soma of the 

 parent which acquired the character in question. 



Dr. Agar sums up the question of transmissible environmental effects 

 as follows : — (1) A changed environment (in its widest sense) may pro- 

 duce a visible variation in the soma indirectly by altering the nature of 

 the metabolic products included in the living protoplasm. These in turn 

 react with the protoplasm, and therefore effect changes in its product, 

 the soma. (2) Whenever the environment acts simultaneously on soma 

 and gonad a similar alteration in metabolic inclusions of somato- and 

 germ-plasm takes place. (3) These metabolic substances included in 



