I 54 fouriial of Comparative Neurology and Psychology. 



The proportionate amount of time spent by the embryos 

 in swimming movements as compared with aimless leg move- 

 ments or in walking movements, becomes progressively greater 

 as development proceeds, during the "trilobite" stage. Dur- 

 ing the period immediately following hatching the embryos ap- 

 pear to become quickly exhausted by violent swimming move- 

 ments. As development proceeds they get stronger until dur- 

 ing the week immediately preceding the first moult after hatching 

 nearly all the time is spent in swimming. 



I have never seen in embryos at this stage any indication 

 of the "forced" gill cleaning reflexes of the gills themseves 

 which occur in the adult, and have been described by Miss 

 Hyde (loc. cit.). 



Movements of the Thoracic Appendages. — When the em- 

 bryos are lying in an inverted position at the bottom the legs 

 ate practically continuously in motion. Immediately after 

 hatching these movements are of the same character as those 

 withiti the "vicarious chorion." The hatched embryo, how- 

 ever, has nothing for the chelae to engage and consequently 

 the movements accomplish no purpose. These leg rnovements 

 are probably still to be regarded as an incipient righting reac- 

 tion (cf. above). Throughout the whole of the "trilobite" 

 stage the embryos do not develop a definite, immediately pur- 

 posiv^e righting reaction like that of the adult. These young 

 embryos right themselves in a great variety of ways and in 

 nearly every case it is a long and tedious process. The most 

 usual way is for one embryo to rather indefinitely push against 

 or crawl over a second individual or a cast "shell" or some bit 

 of debris in the water till it gets righted. The nearest approach 

 to a definite righting reaction which I have seen in these very 

 young individuals is a combination of switnming and leg move- 

 ments. As has been described above violent switnrning move- 

 ments of the gills sometimes serve merely to raise the abdomen 

 of an inverted embryo without causing the animal as a whole 

 to rise from the bottom This results in making the embryo 

 practically "stand on its head" (i. e., rest on the extreme an- 

 terior margin of the cephalothorax). Not infrequently when 



