Pearl, Reactions of Linmlns. 149 



The Behavior after Hatching. 



Appearance of the Orga?iism. — In general form the embryo 

 at this stage closely resembles the adult Linmlns except for the 

 absence of the elongated telson. The appearance of the em- 

 bryo in dorsal and ventral aspects is shown in Fig. i, A and B. 

 This stage is Kingsley's (loc. cit.) Stage K. 



Movement of Abdominal Appendages ; Respiratory Move- 

 ments. — The respiratory movements continue after hatching in 

 the same characteristic manner as has been described above for 

 the preceding stage in development. The only difference in 

 them is found in the rate, which becomes somewhat more rapid. 

 According to my observations the rate of the beat after hatch- 

 ing stands in about the ratio of 5 to 4 to the rate while the em- 

 bryo is within the "vicarious chorion." During some experi- 

 ments in which the embryos were taken from the water and 

 placed on moist sand, with the haemal side uppermost, it was 

 observed in several cases that the respiratory movements con- 

 tinued in the normal manner, while the embryo was out of 

 water. This was a rather unexpected finding, for the reason 

 that adult Limnli never perform continued, normal rhythmical 

 movements except in the water. The only explanation for the 

 case of these young embryos which has suggested itself to me 

 is that possibly at this stage of development the gills are less 

 sensitive to changes in the surrounding medium than they are 

 to the adult. This, however, does not seem very probable, in 

 view of the fact that the general tactile sensitivity of the em- 

 bryo at this stage is greatly in excess of that of the adult. 



Swimming. — Immediately after the embryo leaves the "vi- 

 carious chorion" characteristic swimming movements begin. 

 So far as the abdominal appendages are concerned these move- 

 ments are precisely the same in embryo and adult. They con- 

 sist of strong extensions and flexions of the gills ' with refer- 

 ence to the abdomen. They are rhythmical, and are essentially 



' Throughout the paper where statements are made concerning the perform- 

 ance of swimming movements by the "gills" it will be understood that the gill 

 covers and the operculum are the organs to which reference is made. The term 

 "gills" is used merely to avoid circumlocution. 



