Ill 



PRIMARY INDUCTION EXPERIMENTAL DATA 385 



cer. amp. 



th.ep. 



Fig. 53. Transversal section through the head of the secondary embryo obtained by the 

 operation of Fig. 52. A brain of reduced side is accompanied by a large optic vesicle. Thus, 

 a graft taken in the notochordal area has definitely caused acrogenesis; cer. amp.-cerebral 

 ampulla; mes. -mesenchyme; ret. -retinal layer; tap.-tapetal layer; th.ep. -thickened epiblast. 



From Dalcq and Lallier, 1948. 



discriminative way, including the detection of the stain in sections of the operated 

 embryos. This method allowed an accurate comparison between the presumptive 

 value of the grafts and the structures they yielded and induced. 



Many results of the typical grafts studied by Lallier (Dalcq and Lallier, 1948) and by 

 Minganti (1949) are only of a confirmative nature. However, it remains worth recording 

 that a purely chordomesoblast graft, free of prechordal material, can sometimes induce a 

 head well-provided with prosencephalic structures (Figs. 52, 53). Moreover, an extra- 

 ordinarily narrow fragment, taken from the upper blastoporal lip and consisting only of 

 presumptive pharyngeal endoblast with at most some presumptive prechordal material, 

 produces a complex containing practically all components of an embryonic system 

 excepting optic vesicles and nasal placodes (Dalcq and Lallier, 1948, their p. 347). In this 

 last case, the use of the word "organizer" is certainly defendable. Although this term has 

 ceased to be appropriate for a general designation of induction phenomena, we must not 

 lose sight of the fact that sometimes such an organizing influence is obvious. In both 

 the results obtained by Lallier, the elevatioii of morphogenetic potential is patent; the 

 first operation mentioned is especially interesting since, as in Gallera's experiment (p. 374) 

 notochordal material is partly transformed into prechordal plate. 



Minganti grafted in the ventro-marginal region vitally stained lateral pieces of the 

 organizer, i.e. strictly presumptive mesoblast. With axolotl as with newt embryos, the most 

 frequent cases showed assimilation into the host neighboring tissues, sometimes in situ, 

 more often after an active migration (p. 351) into the mesoblast of the host. Inductions 

 caused by such mesoblastic grafts (with either concordant or inversed polarity) were 

 mainly homoeogenic and, if neurogenic, only evoked a slender spinal cord, never with a 

 cerebral swelling (see also Mookerjee, 1954). 



Benoit (1952) investigated in details the effects of similar grafts, but with 180° reversal 

 of the cephalo-caudal axis. This operation is somewhat analogous to my own rotations 

 in situ of the Discoglossus medio-dorsal zone (p. 381) except that in Benoit's experiment, 

 the implant was put independently either in or above the ventral zone, and he worked 

 with the Urodele egg. The surface of the graft was stained with Nile blue towards the pole 

 (caudal material) and with neutral red toward the antipole, so that the fate of both parts 

 could be easily ascertained by frequent observations. Two results must be mentioned here. 



Literature p. 483 



