346 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 



When a newt blastula or a young gastrula is submitted (Fig. 33) to a meridian ligature 

 (sagittal or frontal) a new blastoporal lip immediately appears at the lesion where the egg 

 wall has been split and more or less crushed, and this lip will be the beginning of a small 

 secondary embryonic system (Dalcq and Huang, 1 948 ; Brice, 1 958) . At least three factors may 

 be involved here: (/) in spite of the drastic deformation, the new lip appears in marginal 

 material which has been intrinsically prepared for ingression, quite possibly by the above 

 postulated mechanism; {2) lesion of the coat has liberated the superficial part of most 

 cells, and facilitates their migration; (j) the wound has apparently some kind of stimulating 

 effect which can increase the metabolism. This is also suggested by the suddenness of the 

 modification. Such a view is in agreement with the fact, observed by Piepho (1938), that 

 the reduction of brillant cresyl blue is accelerated at the level of a slight wound and occurs 

 there as rapidly as in the organizer territory. Thus it seems that in this ligature experiment 

 we have a specific process, which does not use the same mechanism as the progressive 

 formation of the normal blastopore lip. 



0%: 



JV D 



m 



X 



R L 



-8 hours) 



■r 



(+2 days) 



Fig. 33. A case of frontal ligature in a blastula, with regulation of both halves, (a) The 

 germ seen from its vegetal aspect, with marks of Nile blue (coarse hatching) and neutral 

 red (dots). D, dorsal; L, left; R, right; V, ventral, (b) The ligature is made with a hair, 

 at the price of two small wounds (circles). The two parts are now viewed from the side 

 of separation (c,d) the dorsal half; (e,f ) the ventral half, (c) The blastopore of the dorsal 

 half, which has been immediately formed at the place wounded by the ligature; the marks 

 have converged toward the blastopore and have partially migrated inside, (d) The resulting 

 "dorsal" embryo with a still-open and defective neural plate; the Nile blue stain is seen 

 beneath the surface; (e) the blastopore suscitated on the ventral half at the place wounded; 

 (f) the "ventral" embryo, with an elongating tail bud, but a defective head. From coloured 

 drawings by Huang (1948) {cf. Dalcq and Huang, 1948). 



