410 



REMOVAL OF CHICK BLASTODERMS 



EXPLANATION OF CHICK PHOTOGRAPHS* 



Fig. 1 - Embryonic shield, prior to appearance of prim. 



streak. 

 Fig. 2 - Initial streak at 6-7 hours. 

 Fig. 3 - Intermediate primitive streak at 12-13 hrs. 



Fig. 4 - Definitive streak, max. length 1.88 mm. Pr. 



streak, pr. pit, and Hensen's node evident, area 



pellucida pear shaped, incubation age 18-19 hrs. 

 Fig. 5 - Head process stage with notochord, no head fold, 



age 19-22 hrs. 

 Fig. 6 - Head fold stage at 23-25 hrs. 

 Fig. 7 - First somite and neural folds at 23-26 hrs. 

 Fig. 8 - Blood islands forming posteriorly at 26-29 hrs. and 



4 somites. 

 Fig. 9 - Primary optic vesicles, heart primordia fuse, 29- 



33 hrs. , 7 somites. 

 Fig. 10 - Cranial flexure indicated, 3 primary' brain vesicles, 



heart bent at 33-38 hrs. and 10 somites. 

 Fig. 11 - Cranial flexure extensive, 5 neuromeres, optic 



vesicle well developed, heart bent, 40-45 hrs. G 



13 somites. 

 Fig. 12 - Neuropore indicated, telencephalon formed, 



auditory pits, head fold amnion, heart "S" shaped, 



45-59 hrs. and 16 somites. 

 Fig. 13 - Head turned to the left, cranial G cervival 



flexures clear out, head fold amnion present, 48- 



52 hrs. , 19 somites. 

 Fig. 14 - Flexures extensive, body rotating, visceral arches 



forming, 50-53 hrs., & 21 somites. 

 Fig. 15- Lateral body folds, limb primordia, amnion, eye 



cup, 50-55 hrs., 24-27 S. 

 Fig. 16- Wing and leg primordia 51-56 hrs. , G 26-28 S. 

 Fig. 17- Tail bud, epiphysis, 52-68 hrs., 29-32 S. 



♦Some of these photographs were published by Dr. Nelson Spratt in Jour. Exp. Zool. 103:265 and 274; others by Hamburger and 

 Hamilton Jour. Morph. 88:49. All have since been published in Lillic's Development of the Chick, revised by H. L. Hamilton, 

 Copyright Holt, Rinehort and Winston, Inc. 1952, and used here with permission. 



