EXPLANTING AND CULTIVATING 



431 



§-, 



Embryonic parts to be used as explants: 



Stages to be used : 



a. Definitive primitive streak 



b. Head-process stage 



c. Head-fold stage 



d. One to 6 somite stage 



Cuts to be made : (See figure, at the right) 



a. Transversely (i. e. , at right angles to the embryonic 

 axis) about 0. 2 to 0. 7 mm. posterior to the primi- 

 tive pit, using both halves. 



b. Transversely through the primitive pit level, using 

 both anterior and posterior halves. 



c. Transversely anterior to the primitive pit (i. e. , through the early notochord) 

 and simultaneously through the middle of the primitive streak. This gives 

 three pieces of blastoderm, each potentially very different. 



d. Use also whole blastoderms. 



Primitive Streak 

 Stage showing levels 

 of transections. 



THE DIFFERENTIATION OF CHICK EXPLANTS ON VARIOUS TYPES OF MEDIA 



SALINE- 

 AGAR 



SALINE- 

 ACAR 



+ 



VOLK- 



ALBUMEN 



(eNTiRE ECC 

 CONTEmTS) 



(TRACE OF 

 albumen) 



STAGE 

 EXPLANTED 



GENERALIZED RESULTS 



lot HOURS LATER 20i HOURS LATER 



NON~ 



eurfERED 



SALINE- 



AOAR 



+ 



PURE YOLK 



EXTRACT 



^albumen] 



SALINE- 



ACAR 

 + 



YOLK 

 EXTRACT 

 (TRACE OF 



albumen) 



BUFFERED 



SALINE- 



AGAR 



+ 



PURE YOLK 



EXTRACT 



|nO ALBUMEN) 



SALINE- 

 AGAR 



+ 



PURE 



ALBUMEN 



EXTRACT 



(NO yolk] 



lOi HOURS LATER 



J: 



20 1 HOURS LATER 



Development on various media. The sketches are based 

 on camera lucida drawings of the living explants. All 

 ore drawn approximately to the same scale. The num- 

 bers in each block refer to the number of explants. 



•[ i.e. , 20 ± hours after explantation. Only the 

 "■" albumen which adheres to the yolk after the 



ordinary method of separating the 2. The yolk 



was not washed. 



From Spratt 1947: Jour. Exp. Zool. 106:345. 



