190 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



embryo over one half of the egg a fourth week and more and 

 to perfect the embryo for hatching a fifth and sixth week or 

 more. The whole egg development required from five to eight 

 weeks in different sets of eggs under different temperature. 



The heart-beat. — When the embryo has grown so large that 

 it occupies half of the shell and the yolk is correspondingly 

 reduced the beating of the heart is quite conspicuous, more than 

 two weeks before the embryo hatches. Its beat is rapid and 

 may be more than one hundred to the minute and there is the 

 remarkable feature of periodic slowing down and even stoppage. 

 In one embryo the heart beat about 150 times in a minute 

 besides resting some ten seconds so that the rate was very 

 great. There were generally five rests in a minute each of one, 

 two or more seconds each and the intervals between rests were 

 taken up with 26 to 36 beats. 



Hatching-. — The hatching of the eggs as seen in a watch 

 glass with 2-A. took place as follows. The stiff, transparent case 

 within which the embryo has developed splits open along the side 

 next to the embryo's back as a leather ball might if filled with 

 something that expanded. Before this there were seen some 

 muscular movements within the embryo and now the region 

 still containing yolk material was seen to jerk, the antennae 

 now and then contracted in jerks and the legs moved slightly. 

 The back of the creature became more and more exposed to 

 the water, I Fig. 8. The legs showed seeming spasms of con- 

 traction travelling along them and causing local shortenings. 

 The back of the head-thorax and of the abdomen protruded 

 more and more till only the ends of the body and the limbs 

 remained within the shell, II Fig. 8. The larva thus comes 

 into the world back first. In their development the legs and 

 the abdomen have been formed beneath the thorax and bent 

 forward parallel to it, II Fig. 8 ; but now the legs are 

 straightened out and raised up more nearly at right angles to 

 the thorax and the abdomen also is moved backward and this 

 aids in pushing the larva out to the position shown in II 

 Fig. 8. 



These changes have taken some fifteen minutes and after about 

 five minutes more there is a sudden straightening out of the 



