414 



REMOVAL OF CHICK BLASTODERMS 



■ — SOMITE 

 O — ENTODER 

 SR-SINUS 



RHOMBOIDALIS' 

 • —NEURAL CREST 

 LP-LATERAL PLATE 

 M— HEAD MESODERM 



t-HEAHT 

 ©-CHORDA 

 O-NEPMR03 

 •-ERYTHROCYTES 



Prospective areas in the definitive primitive streak blastoderm of the chick. 

 The superficial layer is shown at the left while the invaginated material is 

 seen in the right half. The interrupted line on the left side of the anterior 

 streak region marks the boundary between the ectoderm and the still unin- 

 vaginated mesoderm. This is on the assumptions that invagination is as yet 

 incomplete and that future invagination will be limited to material destined 

 to form the embryo proper. All mesodermal boundaries need accurate ex- 

 perimental verificiation. 



This composite map is drawn by Rudnick (1944 Quart. Rev. Biol. 19:187) 

 and is based largely on work of Pasteels. In addition, there have been con- 

 tributions from the work of Hunt (endoderm cells), Wolff (morphogenesis of 

 trunk and tail), and Yntema (ectodermal placodes). 



Later Embryos: Chick embryos of 36 or more hours of incubation are rather simple to 

 remove from their eggs. The entire egg mass is broken into a finger bowl of saline so- 

 lution cracking the underside of the shell after allowing the egg to remain motionless for 

 several minutes. The embryo, unless it is so far advanced that it is heavy, will float to 

 the upper surface. Excise the embryo as in the manner described above or, if the em- 

 bryo is well formed, grasp the yolk-sac umbilicus with forceps, cut it distally to the 

 forceps, rupture other membranes, and draw the embryo away from its yolk. If the em- 

 bryo is young it may be pulled into a submerged watchglass and transferred to a fresh 

 finger bowl of solution. If it is advanced, it may be transferred in an ordinary teaspoon 

 whose bowl has been perforated with many small holes. 



"Life is the continuous adjitslmeiit uj internal relations 

 to external relations. " 



Herbert Spencer 



"A living organism is both cause and effect in itself. " 



E. Kant. 1892 



