chairman's INTRODUCTION' 469 



endomesoderm formed, (b) larvae with a rather normal ectoderm but the 

 endomesoderm dissolved into large evidently pathological cells, (c) larvae 

 which are animalized, i.e. the whole larva consists only of ectoderm, 

 whereas endomesoderm has not or only incompletely developed. Let us 

 now consider a certain group of cells in the endomesoderm of the normal 

 larva, viz. that marked bv a square in Fig. 2(a). From our experiments we 

 must infer that these cells have the potentialitv both for endomesodermal 

 and for ectodermal differentiation. In the diagram, Fig. 3(^/)' the larger 

 horizontal \ector (^ eg) indicates the pathway of syntheses which have a 

 specifically endomesodermic trend. The opposite horizontal smaller 

 vector (An) represents a pathway for syntheses which have an animal or 

 ectodermic trend. Moreover there are other vectors that represent trends 



(b) 



(c) 



¥lG. 2. ia), {h), (r), three possible alternatives of differentiation in eygs that had 

 been pretreated in the unfertilized stage with 6-5 x lo"^',, trypsin. In (a) develop- 

 ment is normal, a certain region marked by a square becomes normal endoderm. 

 In (b) the ectoderm forms a continuous layer that presents a lower degree of 

 differentiation than (a). The endomesoderm is dissociated in rounded cells. The 

 region corresponding to the marked region in (a) consists of dissociated cells showing 

 tendency for cytolysis. In (c) ectodermization or animalization has occurred. The 

 marked cells again constitute an epithelium but this has ectodermic character. 

 Some few mesenchyme cells appeared. 



that are common to cells on all le\els in the larva. The \egetal pathwav 

 dominates in this region but the animal pathwav is not suppressed 

 altogether. It contributes to the character of the cells on this level. In this 

 wav one explains the fine gradation in the properties and beha\"iour of the 

 cells which Dr. Gustafson has demonstrated and certainly will refer to 

 later today. In larvae of the tvpe of Fig. 2{a) no injurv was observed, 

 whereas in a larva of the type Fig. 2{b) the threshold of injury evidently was 

 low. In the larval region marked by the square protein synthesis gradually 

 became blocked, with ensuing dissociation of the cells gradually followed 

 by cytolysis. The break up of the synthetic pathways is also indicated 

 diagrammaticallv in Fig. T,{b). The larvae of type Fig. 2(r) demonstrate 

 however, that the vegetal pathway evidently has a lower threshold than 

 the animal one. The vegetal pathway mav now be eliminated (jr reduced. 

 In this way animalization results, cf. also diagram, I-'ig. t,{c). W'q find that 



