1 56 /oiinial of Comparative Neurology and Psychology. 



water by lifting the needle. This reaction cannot be induced 

 immediately after hatching, and only reaches its greatest per- 

 fection towards the end of the "trilobite" stage. It is a very 

 definite and striking piece of behavior and may be induced 

 with perfect certainty at every trial in late "trilobite" embryos. 

 It can apparently only be classified as a form of thigmotactic 

 reaction, and seems to me to be significant chiefly in indicating 

 the degree of coordination in leg movements which has de- 

 veloped since hatching. What, if any, significance such a re- 

 action can have in the life of the embryo under the normal con- 

 ditions of existence I am unable to conjecture. It seems to be 

 merely a reaction very perfectly adapting the embryo to the 

 business of climbing up slender sticks or needles, and, so far as 

 I know, there are no natural demands in the normal existence 

 of the animal at tnis stage of development which would make 

 such a reaction either necessary or even useful. I observed 

 this reaction as first occurring about one week prior to the time 

 of the moult which ends the "trilobite" stage. 



Walking Moi'ejnents. — Immediately after hatching the 

 walking movements are very irregular. There is apparently 

 little coordination between the different legs, and as the animal 

 progresses it rocks and sways from side to side and frequently 

 falls over on one side. As development proceeds the move- 

 ment becomes somewhat better coordinated. This form of loco- 

 motion is, however, even in the adult, a poorly coordinated 

 one, the organism being much better adapted to swimming 

 than walking. The embryos got on better when walking on a 

 roucfh surface like the sand bottom, than on a smooth surface 

 like glass. 



Avoidanee of Obstacles in the Path. — Neither when walking 

 nor when swimming do embryos show any perception of an ob- 

 stacle in the path before they strike it. 



If a very young embryo when walking strikes an obstacle 

 like a needle held in its way, no attempt is made to get around 

 it. Instead, the embryo will continue to walk straight ahead 

 pushing the anterior margin of the cephalothorax against the 

 obstacle. This action will be continued till, by chance, in the 



