CONTENTS 



Pago 



I nt roduction 111 



Stages in normal development 112 



Materials and methods 112 



Description of stages 113 



Stage 0: Ovulated but unfertilized egg 114 



Stage 1: Zygote 114 



Stage 2: Two cells 115 



Stage 3: Four cells 116 



Stage 4: Eight cells 116 



Stage 5: Sixteen cells 117 



Stage 6: Thirty-two cells 117 



Stage 7: Sixty-four cells 118 



Stage 8: Full blastula 118 



Stage 9: Gastrula 119 



Stage 10: Neural plate and groove 120 



Stage 11: Neural rod 121 



Stage 12: Head 122 



Stage 13: Prehatching 123 



Stage 14: Hatching 123 



Stage 15: Pigmentation 124 



Stage 16: Gill clefts 125 



Stage 17: Burrowing 126 



Stage 18: Larva 127 



Review of stages and comparison with earlier studies 128 



Development at different constant temperatures 130 



Materials and methods 130 



Account of individual experiments 132 



Development at 45° F 132 



Development at 50° F 133 



Development at 52.5° F 134 



Development at 55° F 134 



Development at 60° F 135 



Development at 65° F 137 



Development at 70° F 138 



Development at 75° F 139 



Development at 77.5° F 140 



Development at 80° F 140 



Significance of observations 141 



Effect of temperature on development 141 



Literature cited 142 



