226 'Journal of Comparative Neurology and Psychology. 



were earing the moulting-period and preparing to pass into the 

 second stage. 



Experiment ly — July 17, 8 -.7^0 a.m. About one hundred fourth- 

 day, first-stage lobsters (Group A) were taken from one of the 

 hatching bags and placed in the glass jar in the dark box. The 

 majority reacted positively to daylight through the small window. 

 At I o'clock, when examined again, about one-half of them 

 were reacting negatively. The jar was then removed and placed 

 in the light of the west window where the intensity was greater. 

 At once every larva became negative in reaction. 



In order to determine whether this mode of reaction was a nat- 

 ural incident in the life of the larvae of this age, or whether the 

 response had been induced as a result of their having been so 

 long subjected to experimentation, twenty-five first-stage larvae 

 (Group B) were removed from the same group as that from which 

 the larvae mentioned above were taken. When these twenty- 

 five were put in a glass jar and placed in the west window beside 

 the group mentioned above, they gave a positive reaction. After 

 five minutes, half were positive and half negative. At 5:30 the 

 «un was low and the light weak, but all the larvae gave a negative 

 reaction, which persisted, as did the negative response in Group A 

 mentioned above, until far into the twilight. 



It may be further noted in this connection, that five of the larvae 

 which reacted negatively in the afternoon were placed in abso- 

 lute darkness for four and a half hours. It was believed that the 

 positive reaction might be renewed; but this was not the case when 

 they were again brought into daylight of several intensities. 



Experiment 18. Case I — July 20, 4 p.m. A number of fourth- 

 day, first-stage larvae were removed from the hatching bag and 

 put in the glass jar. This w^as placed in the dark box and the 

 larvae submitted to red Hght through the three by three inch win- 

 dow. The resulting reaction was positive and remained so even 

 when the intensity was still further diminished by inserting num- 

 erous sheets of paper behind the red glass. Finally, a point was 

 reached where the positive orientation was lost and a homogeneous 

 scattering occurred. When the intensity of the light was again 

 increased, the positive orientation returned; but, with a still 

 greater increase in intensity, this response became again less defi- 

 nite, and finally, in the more intense blue and white light, the neg- 

 ative reaction again appeared. 



