12 THE YOUNG OF THE CRAYFISHES ASTACUS AND OAMBABUS 



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showed that the eggs are carried by the female all the winter and hatch in the 

 spring. The eggs on each female were about 500 in number and formed a dark 

 brown or more usually nearly black mass all over the under side of the abdo- 

 men. Each egg was very large, about 2.5 mm. in diameter, and as in other 

 kinds of crayfish, enclosed in a complete capsule of hardened secretions that ex- 

 tended as a slender stalk to fix each to the setae on the pleopods, or, in some 

 cases, to the setae on the sternal ridges of the abdomen. All the eggs seemed 

 in good condition except a cluster of four or five among the brown eggs of 

 one female and these few were overgrown with a fungus. 



The darker eggs plainly showed embryos in the stage represented by 

 Keichenbach ('86) as J, fig. 12, standing out as a whitish area on one side of 

 each egg. Thus the embryo had already advanced to a condition in which the 

 embryonic area occupied a considerable part of one-half of the spherical egg. 

 There was still a wide margin between the appendages and the well elevated 

 wall that surrounded all the posterior part of the embryo. The eyes, two pair 

 of antenna 1 , mandibles, maxillae, maxillipeds, and five ' periopods were well 

 marked. The posterior four periopods and the abdomen projected forward 

 over the thorax so that the abdomen reached to the first maxilla 1 . The eggs 

 of one female showed in addition to the above embryo many nuclei scattered 

 over the nonembryonic areas of the egg and plainly seen against the brown 

 background of yolk. 



In one female the eggs were covered by a dark deposit that had to be 

 scraped off before the glossy egg capsule and the contained embryo could be 

 seen. 



A few eggs were greenish and covered by a deposit that could be scraped 

 off; when these were opened, or when boiled, the contained embryo was found 

 to be in the stage II of Reichenbach. 



In one black egg the heart of the embryo was seen to beat very faintly, 

 and after the eggs had been kept in water twenty-four hours many eggs showed 

 the heart beating and were kept in the hope that they would develop. In water 

 about 9 C. the eggs that were still attached to the abdomen of living females 

 did develop, though very slowly, as will be seen from the following results. 



After nine days, March 2, the embryos were perceptibly enlarged with 

 longer antenna? and abdomen, the second antenna? reaching back nearly half way 

 to the end of the limb-bearing region. The heart, now lying in a plane at right 

 angles to the ventral surface and above the base of the abdomen, was beating 

 so strongly as to give a decided jerk to the thoracic limbs. In one embryo it 

 beat at the rate of 66 to the minute and in another at 82. Inside the outer egg 

 capsule there was evidently a delicate inner membrane investing the embryo. 



For six days more the only change noted was a slight increase in size and 

 the extension of the second antennnc beyond the middle of the limb-bearing 

 region. 



