THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS 13 



Four days later a marked widening of the anterior part of the embryonic 

 area had taken place and the slow growth of the abdomen had brought its tip 

 up to the posterior edge of the mouth. In another week the still larger em- 

 bryos had antennae reaching nearly to the end of the depressed, limb-bearing, 

 region and the abdomen reached forward over the mouth as far as the bases of 

 the second antenna\ 



Embryos of this age, some twenty- five days after they were received, were 

 very attractive objects seen through the transparent egg capsules. The trans- 

 parent limbs stood out strongly contrasted against the dark red yolk mass that 

 still took up the major part of the spherical egg. On each side of the egg the 

 boundary of the yolk mass was slightly incised where the "liver" was forming. 

 When such embryos were plunged a moment into boiling water and then put 

 into cold water a mere scratch of a needle sufficed to cause the tough outer 

 capsule to open with explosive force and the embryo was readily removed, leav- 

 ing even its thin membrane sticking to the inside of the capsule. 



During another week there was but little increase in the length of the ap- 

 pendages, but through the transparent walls of the limbs and body a few blood 

 corpuscles were seen passing along in the large median thoracic artery and 

 in the antennae and periopods. 



Ten days later, April 5, when the water had risen from 9 to 11, the size 

 had markedly increased and the embryo instead of being restricted to a flat 

 region upon one side of the sphere could no longer be seen from a single point 

 of view, since it now extended in a curved surface over one-half of the egg. The 

 long antennae now met one another and their tips overlapped at the deep notch 

 where the abdomen joined the thorax. The legs and chelae had grown long 

 enough to overlie the abdomen and to conceal its tip. Such embryos were 

 nearly in the stage K of Eeichenbach and were prettily colored. The carapace 

 had bright red pigment along its ventral border, the dark red-brown yolk took 

 up less than half the bulk of the egg and was divided by a deep fissure into an- 

 terior and posterior lobes which were encroached upon by the "liver" which 

 was conspicuously colored. In one its contents were red and in fifteen green- 

 ish and translucent or else white-yellow and opaque. The large eyes had also 

 some pigment formed in them. 



Eleven days later the elongated walking legs and chelae reached forward 

 over the posterior edges of the eyes. Pigment cells were as yet not seen in 

 the above limbs, but were conspicuous in the first and second antennas and in 

 the abdomen as well as the thorax. The delicate inner membrane was seen 

 loosely investing the tips of the chelae like a cast-off exoskeleton. 



Some six days later the embryo had passed beyond the stage K and was 

 nearly ready to hatch. The limbs were even longer, so that the chelas reached 

 over part of the eyes and the antennae overlapped one another the whole width 



