296 DARWINISM TO-DAY. 



d'abord produit ; il se transmet a des descendants dont la coquille 

 est deroulee ! C'cst done que le patrimoine hereditaire a ete 

 modific sous I'influcnce dc la production mecaniquc de ce sillon' 

 dorsal, an point de devenir adequat a cette forme nouvelle d'equi- 

 libre ; il y a un nouveau patrimoine hereditaire, qui construisant un 

 individu nouveau et son squelette. fera apparaitre, sans pression, 

 le sillon dorsal !" 



The results of the experiments of Cunningham on flatfishes are 

 stated by the author, in a paper on "The Problem of Variation." 

 Nat. Sci., Vol. Ill, p. 285, 1893. Cunningham put the very young 

 fish, while still bilaterally symmetrical (in which stage the pigment 

 is equally developed on both sides of the body), into aquaria lighted 

 from below. He found that when the young fish begins to undergo 

 its metamorphosis, the pigment gradually disappears on one side, 

 as it would have done under normal conditions, i. e., when they are. 

 lighted from above. If, however, the fish are kept for a short time 

 longer, lighted from below, the pigment begins to come back again. 

 "The first fact," says Cunningham, "proves that the disappearance 

 of the pigment-cells from the lower side in the metamorphosis is a 

 hereditary character, and not a change produced in each individual 

 by the withdrawal of the lower side from the action of the light. 

 On the other hand, the experiments show that the absence of pig- 

 ment-cells from the lower side throughout life is due to the fact that 

 light does not act upon that side, for, when it is allowed to act, 

 pigment-cells appear. It seems to me that the only reasonable con- 

 clusion from these facts is that the disappearance of the pigment- 

 cells was originally due to the absence of light, and that the change 

 has now become hereditary. The pigment-cells produced by the 

 action of light on the lower side are in all respects similar to 

 those normally present on the upper side of the fish. If the dis- 

 appearance of the pigment-cells was due entirely to the variation 

 of the germ-plasm, no external influences could cause them to re- 

 appear ; and if there were no hereditary tendency, the coloration 

 of the lower side of the flatfish would be rapid and complete." 



Concerning Fischer's highly interesting experimental work, I 

 quote the following paragraph from Fuchs, H. (Biol. Centralbl., 

 Fischer's ex- Vo1 - XXI > PP- 591-592, 1901; Fischer's own papers 

 periments with have been published in various biological journals, 

 butterflies. t ne particular one recounting the results obtained 



with Arctia caja in the Allg. Zeitschr. fur Entomologie, VoL 

 VI, 1902) : 



"Experimentelle Untersuchungen, ob es moglich sei, durch will- 

 kiirliche, geeignet gewahlte Veranderungen der 'ausseren Lebens- 

 bedingungen,' besonders der Temperaturverhaltnisse, im Tierreiche- 



