I 52 Journal of Comparative Neurology and PsycJiology. 



swim from the upright position. As will be described in detail 

 later, the embryos are able under certain conditions to right 

 themselves after hatching. It very frequently happens with 

 the youngest embryos that an individual in the upright position 

 (i. e , with the neural side down) will suddenly start violent 

 swimming movements with the gills. When this happens the 

 embryo immediately moves forward and upward away from the 

 bottom. For a short distance (varying in different cases) it 

 maintains the upright position while free in water, but in a very 

 short time after starting in every case it topples over and falls 

 into the normal position for swimming, that is with the haemal 

 side down. It then continues swimming in quite the normal 

 way. 



As development proceeds the swimming becomes better 

 controlled and the embryo gains the power of rising from the 

 bottom by swimming without first turning over. The earliest 

 stage at which I have seen embryos do this was about forty- 

 eight hours after hatching. Even at this time the embryos do 

 not rise directly from the bottom, but first slide along the bot- 

 tom for a distance of from three to five centimeters and then 

 gradually veer upward. In about a week after hatching the 

 swimming is under perfect control in all cases. The animals 

 rise at once from the bottom, and direct the movement quite as 

 well as does the adult. Apparently the only difference between 

 embryos of this stage and adults with respect to the swimming 

 is in the fact that the legs remain quiet in the case of the em- 

 bryo. 



A problem in connection with the swimming movements 

 in the embryo in which I was especially interested was this : 

 Why is it that swimming movements of the gills appear imme- 

 diately after hatching, while before that time no indication of 

 such movements are to be observed ? The most probable ex- 

 planation seemed to be that the swimming was a purely reflex 

 movement which needed the stimulus of the normal sea-water 

 on the sense organs of the gills to set it into accion. In other 

 words, the reflex mechanism was complete in the embryo be- 



