No. 473] 



EGG-LAYING OF CRAYFISH 



345 



middle of the abdomen. The small limbs of the abdomen, the 

 pleopods, swung slowly back and forth with interruptions and 

 then, after three minutes, flapped actively back and forth. Three 

 minutes later the crayfish gave up this attitude and crouched 

 down and turned slightly over to one side while still swinging 

 the pleopods and also making very active fanning movements 

 of the exopodites of the maxillipedes. After four minutes the 

 crayfish again stood up and swung the pleopods back and forth 

 for five minutes and then a faint halo of glaire was first detected 

 about the pleopods. The abdomen had now become bent for- 

 ward in a curve so that it resembled a half-closed hand and the 

 space so enclosed seemed filled with an almost invisible glaire. 

 When the pleopods inside this mass moved there resulted a jerky 

 movement of dirty lines where the glaire and water met at the 

 anterior opening of the chamber formed by the bent abdomen. 

 Two minutes later the animal ceased to stand up and lay upon 

 its left side with all the right legs high in the water, but after lying 

 thus for two minutes it turned onto its ventral side and crouching 

 prone, raised its third, fourth, and fifth legs on the left side, but 

 coming against the side of the dish, did not roll over onto its right 

 side as was expected. By this time the long continued and increas- 

 ing contractions of the muscles of the abdomen had flexed it so 

 far forward that the tail-fan reached to the bases of the second 

 thoracic legs, leaving only the mouthparts and the bases of the 

 chela? and second legs exposed to view. The pleopods were 

 still moving rapidly back and forth inside the glaire chamber. 

 Two minutes later, some of the legs on the right side were raised 

 and the animal seemed about to turn over onto the left side but it 

 returned to the ventral position. The abdomen had now become 

 flexed even more powerfully so that its terminal piece, the telson, 

 reached to the bases of the chelae, or first thoracic legs, and it was 

 pressed upward against the thorax so that some of the slightly 

 turbid glaire was forced out from between the tail-fan and the 

 thorax. With the abdomen thus carried forward under the thorax, 

 the animal remained six minutes crouching down so that anteriorly 

 the ventral side of the thorax was near the bottom of the dish 

 while posteriorly the dorml side of the abdomen rested upon the 

 bottom. Then all the right legs were raised and the body slowly 



