Pearl, Reactions of Limuhis. 143 



tion of the movements of the embryo within the "vicarious 

 chorion" the abdominal appendages will be considered first, as 

 the phenomena here are relatively simple in character. 



The abdominal appendages (operculum and gills) begin 

 characteristic, rhythmical respiratory movements at least five 

 days before hatching. It is probable that in reality such move- 

 ments begin even earlier than this, but I have no observations 

 going farther back. The ordinary respiratory movements when 

 first observed are precisely like the same movements in the 

 adult Limulus. They consist of a rhythmical, up-and-down 

 beating of the gills, each gill book being opened during the 

 phase of expansion, or "inspiratory" phase, to adopt the term- 

 inology of Miss Hyde ('94). 



There is, however, one significant difference in the respira- 

 tory movements of embryos and adults. This is in the 

 rate. In the adult the normal rate is about twenty-five to 

 thirty beats per minute. In the embryos the rate is markedly 

 more rapid, the average number of beats from my observations 

 being sixty per minute. The range of variation is from 55 to 

 60 beats per minute. The rhythm of the beats is quite as per- 

 fect in the embryos as in the adults. 



These respiratory movements are the only movements 

 which the abdominal appendages perform before the embryo 

 leaves the "vicarious chorion," so far as I have observed. I 

 was never able to detect any tendency towards swimming move- 

 ments of the gills before the time of hatching, although the 

 embryos were under observation for six or more hours every 

 day, and especial attention was paid to this point. This absence 

 of swimming movements is rather remarkable in view of the 

 fact that all the embryos begin swimming immediately after 

 hatching. 



In addition to the swimming movements the complex 

 "gill-scraping" reflexes are absent, according to my observa- 

 tions, in embryos prior to the time of hatching. Certain of these 

 reflexes have been described by Miss Hyde (1. c. p. 432, and 

 Fig. 3). There also occur in adult Liinuli, under certain con- 

 ditions, complex gill-scraping movements of the sixth legs. I 



