November 24, 1905.] 



SCIENCE. 



G77 



second and third stage larvae under similar 

 conditions of light and background. 



EXPERIMENT IV. 



Conditions: icliite hackground; red monochro- 

 matic light; 20 first stage larvce. 

 Test. Lt. Eud. Mid-area. Dk. End. Cover. 



1 2 1 17 



2 2 3 15 



3 3 4 13 Reversed. 



4 6 2 12 



EXPERIMENT V. 



Conditions: white hackground; blue monochro- 

 matic light; 20 first stage larvce. 

 Test. Lt. End. Mid-area. Dk. End. Cover. 



1 12 4 4 



2 11 3 6 Reversed. 



3 13 2 5 



These two experiments indicate that in the 

 case of a v?hite background and red monochro- 

 matic light, the first stage lobsters are nega- 

 tively phototropic, v^^hile in the case of a vphite 

 background and a blue monochromatic light the 

 same lobsters are positively phototropic. This 

 was naturally somewhat unexpected, but in all 

 the experiments involving similar conditions 

 of light and background, the second and third 

 stage lobsters respond in a similar manner. 

 In case, however, a black background is used 

 with lobsters of the first three stages, numer- 

 ous experiments demonstrate a negative photo- 

 tropism under the conditions of both red and 

 blue light. 



EXPERIMENT VI. 



Conditions: black background; 20 early fourth 



stage lobsters; sunlight bright. 

 Test. Lt. End. Mid-area. Dk. End. Cover. 



1 13 3 4 



2 15 3 2 Reversed. 



3 12 4 4 



4 15 4 1 



When experiments were tried with the 

 fourth stage, however, a different reaction was 

 found to occur. On black backgrounds and 

 with lights of any intensity or color, the 

 fourth stage lobsters appeared, contrary to the 

 first three stages, positively phototropic, as the 

 following table demonstrates. The degree of 

 light intensity made no further change in the 

 results, save that in instances where the light 



was the least intense the reaction was least 

 marked; and when the light was most intense, 

 as obtained by reflecting rays of light by 

 means of a mirror into the tube, the definite- 

 ness of reaction was most evident. 



When white backgrounds were used in con- 

 nection with the fourth stage lobsters, it was 

 found that in every case except with the 

 monochromatic red light, a positive photo- 

 tropic reaction resulted. The latter, which 

 was also contrary to expectations, may be out- 

 lined as follows: 



, . EXPERIMENT VII. 



Conditions: white background; monochromatic 



red. light ; 20 early fourth stage lobsters. 



Test. Lt. End. Mirt-area. Dk. End. Cover. 

 18 5 6 



2 1 6 13 Reversed. 



3 1 10 9 Reversed. 



4 4 5 11 



These resulting reactions in the case of the 

 early fourth stage lobster may offer an ex- 

 planation for the fact that this stage is so 

 frequently caught in tow-nets drawn over the 

 surface of any of our shore waters, while it 

 has been a very unusual occurrence to secure 

 in this manner either the earlier or the later 

 stages. The same causes may also have worth 

 for the reported facts that certain stages of 

 the free-swimming larvae of other forms of 

 Crustacea are found more frequently at the 

 surface than are other larval stages of the 

 same species. 



It was a noteworthy fact, however, that old 

 fourth stage lobsters would never manifest 

 positive phototropic reactions with the same 

 degree of certainty as that demonstrated in 

 the case of younger fourth stage lobsters. 

 Indeed, in a number of instances, fourth stage 

 individuals which were due to molt within 

 a period of one or two days, manifested on 

 black backgrounds a definite tendency towards 

 a negative phototropic reaction. This re- 

 sponse was assumed without exception after 

 the lobsters had molted into the fifth stage, 

 and this reaction was manifested with any 

 combination of light intensity, color or back- 

 ground. The following tables show the reac- 



