144 /ounial of Comparative Ncnro/ogv and Psychology. 



have never seen these in the embryos before the time of hatch- 

 ing. 



The intervals of rest in the respiratory movements, which 

 in the adult occur frequently and may last for an hour at a time, 

 are much less frequent in their occurrence in the embryos, and 

 do not continue for such long periods. 



For some time before hatching the thoracic appendages 

 can be seen to be making active movements almost continu- 

 ously. These movements vary greatly in force in different in- 

 dividuals, and at different times with the same individual. 

 When they first appear they are usually very weak and increase 

 in violence as development proceeds. At first it was thought 

 that these movements were entirely random and aimless in char- 

 acter. They appeared to consist entirely of mere wavings and 

 stretchings of the legs. Closer observation showed, however, 

 that they were rather more definite than at first appeared. It 

 was seen that they were the cause of the curious translatory 

 movements of the egg as a whole. As the time of hatching 

 approaches one notices very frequently that a particular egg 

 lying by itself on the level, smooth bottom of a glass dish will 

 suddenly begin to move, and slowly roll along the bottom, usu- 

 ally in a straight line. Frequently an egg will roll several cen- 

 timeters in this way, although usually it does not cover more 

 than from one to two centimeters. 



These translatory movements of the egg as a whole are 

 caused by the movements of the thoracic appendages in the 

 following way. As the animal lies in the bottom of the "vicar- 

 ious chorion," in the manner already described, the anterior and 

 lateral margins of the cephalothorax are in fairly close contact 

 with the inner surface of the "vicarious chorion." At this 

 stage the chelae of the walking legs end in very sharp points. 

 As a result of these two conditions, when the legs are extended 

 the points of the chelae catch on the insid^ of the "vicarious 

 chorion." The legs are usually directed somewhat forward 

 when they are extended, and as a consequence of this and of 

 the normal anatomical position of the legs it follows that the 



