260 Jourtial of Comparative Neurology and Psychology. 



rotations. From these facts it may be assumed that the twihght 

 swimming of the larvae probably represents the natural behavior 

 or at least the behavior that arises purely from the internal states 

 themselves; and that the peculiar antics characteristic of the day- 

 light swimming represent a type of behavior chiefly due to the 

 action of external stimuli. 



The question now naturally arises — Do the various turnings, 

 rotations, leanings, and fallings which constitute the appar- 

 ently haphazard behavior of the larval lobsters when swim- 

 ming in daylight or other brilliant illumination, give any indica- 

 tion of method } Observations have given a suggestion as to the 

 means whereby we may attempt to ascertain the value of certain 

 light-conditions in determining these peculiar forms of behavior.^ 



If larval lobsters of any of the first three stages are subjected 

 to the influence of light which comes from one direction only, as 

 from the side, the first fact observable is that the larvae undergo a 

 certain body-orientation; they turn away from the light and place 

 the long axis of the body parallel to the direction of the rays. The 

 second fact which may be noticed is that the larvae move in the 

 direction of the light rays either toward or from the source of 

 illumination. A third fact, which is of prime importance and 

 which involves those stated above, is that no matter whether the 

 progressive movement of the larvae be toward or away from the 

 source of light, the orientation of the body (head away from the 

 source of light) remains unchanged. To state the matter briefly 

 we may say that, whatever the nature of the progressive orienta- 

 tion of the larvae, the body-orientation is at all times, and under 

 all conditions, negative. BoHN (1905, p. 8) has clearly pointed 

 out this fact for the larvae of the European lobster. In this regard 

 he says: "En general, les larves de homard se placent dans le 

 sens negatif; meme, dans les premieres heures apres I'eclosion, alors 

 qu'elles se groupent vis-a-vis des lamps, leur tete se tourne du 

 cote oppose, et les larves s'approchent de la lumiere en regardant 

 I'obscurite, c'est-a-dire en reculant. Ainsi, apres I'eclosion, 

 I'orientation a lieu dans le sens negatif, mais le deplacement se 

 fait dans le sens positif. Dans le suite, si le sens de I'orientation 



'' Many of the observations which follow were made previous to the writer's knowledge of the excellent 

 work of Georges Bohn (1905) along similar lines, upon the larva? of the European lobster, Homarus 

 vulgaris. The writer would acknowledge, however, his great indebtedness to this investigator, whose 

 work has proved suggestive in the highest degree, and whose observations on the mechanics of behavior 

 the writer has been able, in the majority of instances, to verify as well as supplement. 



