VII. Transmission of environmental effects from parent to offspring in simocephalus vetulus

Abstract

Two distinct sets of phenomena can be distinguished, each of which gives the appearance of the inheritance of acquired characters. Somatic induction (Detto; = "Somatische Reizleitung” of Plate) corresponds to Lamarckian inheritance in its strictest sense, where the soma acquires a certain character in response to a certain stimulus, and then influences the germ plasm in such a way as to cause it to produce offspring exhibiting the same character even in the absence of the special stimulus that was needed to produce it in the ancestor. Parallel induction (Detto; = “Simultanreize” of Plate) is applied to cases in which the same external stimulus affects both germ plasm and somatoplasm in the same way, simultaneously but independently. Whereas probably most zoologists think that the existence of somatic induction has not been demonstrated, many well-established cases of parallel induction have been described. Probably all cases of persistence of the effects of a previous environment on offspring bred in a different environment also come under this heading. In the following pages I have described some experiments on parallel induction carried on on a large scale and with measurable characters, lending themselves therefore to biometrical treatment. Special attention has been paid to the all important subject of controls, as will be described in the proper place. The organism I have employed is Simocephalus vetulus , a common Daphnid which adapts itself easily to breeding in captivity.