124 CARNEGIE INSTITUTION OF WASHINGTON. 



were reared in the light and in the dark. Those developing in the 

 vivarium were fairly black, as tadpoles of this species normally are, 

 while those reared in the cave had very little pigment except in the eyes, 

 and were so transparent that the heart and larger blood-vessels in the 

 head and tail regions were visible externally. These larvae and larvae 

 of the common spotted salamander, Ambystoma pundatum, when 

 reared in the dark, have so little pigment that they resemble the cave- 

 fish in the soft pinkish-white general body-color and in the reddish 

 appearance of the heart region due to the large amount of blood showing 

 through the transparent tissues. Again, this season msmy Ambystoma 

 'punctatum have been reared in the cave. One is struck by the relative 

 lack of pigment in most individuals of this species developing in dark- 

 ness. It requires close scrutiny to detect any pigment whatever, except 

 in the eye. In every case, however, as the period of transformation 

 approaches, the light individuals begin to develop pigment and by the 

 time transformation is completed even the lightest individuals, though 

 kept in the dark all the time, have developed a normal pigment com- 

 plement. The Ambystoma opacum larvae reared in darkness developed 

 a reduced amount of pigment as compared with those reared in day- 

 light, but the reduction is not nearly so large as with A. punctatum. 

 Spelerpes hilineatus larvae reared in darkness show only a comparatively 

 slight reduction in pigment development. Species and, to some extent, 

 individuals, show a marked difference in the amount of pigment reduc- 

 tion produced by developing in darkness. Ainhy stoma punctatum is 

 very susceptible to the effect of darkness and develops very little 

 pigment. Ambystoma opacum is much less influenced by the lack of 

 light, and Spelerpes bilineatus is only slightly influenced. 



Considerable numbers, both of the cave form and of the outside 

 form, of the amphipod Eucrangonyx gracilis have been kept in the 

 cave and in the vivarium. The cave form has no pigment except in 

 the eyes, while the outside form has the normal amount of pigment for 

 a crustacean. Young of the outside form, made to develop in the cave 

 and consequently never exposed to dayhght, have nevertheless formed 

 body pigment in some cases and in others have no pigment except 

 in the eyes. The young are only two-fifths grown and all may yet 

 develop pigment. None of the series kept in the cave and derived 

 from ancestors living outside caves has developed even approximately 

 as much pigment as individuals of like size kept in daylight. 



The work upon a comparison of the light and tactile reactions of the 

 cave form and the above-ground form of this amphipod was completed 

 while in Indiana in February. The results show conclusively that the 

 cave form is considerably more reactive to tactile stimulation than the 

 outside form. A definite measure for this difference in reactiveness 

 was used and the results were obtained in precise terms. On the other 

 hand, the cave form is somewhat less reactive to photic stimulation 



