140 CARNEGIE INSTITUTION OF WASHINGTON. 



stated in last year's report (p. 132), one line (line 757) showed a marked 

 divergence in the strains selected for greater and for less reactiveness 

 respectively. Further analysis has brought out additional points: 

 (1) Environmental influences, which much affected the mean reaction- 

 time in all the lines studied, in the line in which an unmistakable se- 

 lective effect was obtained, merely served to cut down the divergence 

 temporarily; (2) the result, divergence in reactiveness, is due to changes 

 in the reactiveness of both the high and low strains of the line affected; 

 (3) the form of the reaction-time curves indicates that the effect was 

 cumulative and that the divergence was still increasing when selection 

 was discontinued ; (4) the result appears to be due to many small genetic 

 changes; (5) the two strains of the line are indistinguishable, except in 

 their differences in behavior to directive light stimulation; (6) the di- 

 vergence is permanent, or at least persisted 112 generations (32 months) 

 after selection was discontinued. 



EFFECT OF CAVE CONDITIONS. 



For some years Dr. Banta has been breeding animals under cave 

 conditions to ascertain the change in color, or possibly form, that may 

 result, in the hope of throwing some light upon the extraordinary char- 

 acters of cave animals. Amphipods are breeding freely under our 

 cave conditions. Additions to our cave fauna are being made each 

 spring. 



MUTATIVE COLOR CHANGES IN FLOUNDERS. 



An observation which has interested Dr. Banta concerns the occur- 

 rence of pigment on both sides of the common flounder in Cold Spring 

 Harbor. During this summer apparently about 20 per cent of the 

 fish, which are presumably of this year's (early spring) hatch, possess 

 more or less pigment on the side upon which the fish rests and which 

 is normally entirely without pigment. Fishermen agree that they had 

 never commonly seen ''flatfish with black on both sides" until the 

 present season, though they claim to have seen them occasionally be- 

 fore. In an examination of all the larger flatfish available (only a few, 

 however) which were presumably of a previous year's hatch, only one 

 with any trace of pigment on the under side was found. The pigment 

 in this case consisted of a mere trace on the caudal fin and in the lateral- 

 line region of the tail. The pigment on the under side in the smaller 

 fish varied all the way from a mere trace caudally to complete pigmen- 

 tation of the under side, except for the head and a small portion 

 immediately posterior to it. All specimens were fully pigmented on 

 the upper side, which bears both of the eyes. 



PHYSIOLOGY OF REPRODUCTION AND DEVELOPMENT. 

 EFFECT OF VARIATIONS OF OXYGEN-SUPPLY ON AVIAN DEVELOPMENT. 



In connection with his sex studies. Dr. Riddle has found it necessary 

 to undertake or to continue the examination of certain factors or con- 



