EMBRYONIC RECONSTITUTIONS 



519 



regards the Bildungscentnim, how does a substance diffusing from this 

 center activate or determine an axiate pattern with region of greatest de- 

 velopmental activity near the anterior end of the future embryo, that is, 

 farthest away from the source of the substance? A complete Hgature in 



^ Porsal Surface. 



•ApleriOrSujAlCe \ ,— Cauda/ P.'ale 

 ^ L ^ 



Meoa/ 



Max. ilfae 

 ProfJ^orax 



?fetal};oratc 

 Tfesofjporax 



^-Veplral Sur/ctce 



Fig. 166, ^-£.— Differential modification of development by KCN in the coleopteran 

 Bruchus quadrimaculatus. A, diagram of a median longitudinal section showing surfaces and 

 presumptive embryonic regions; B, ventral view of early stage, indicating by density of shad- 

 ing the differential susceptibility to KCN, decreasing from the median maxillar-prothoracic 

 region posteriorly and laterally; C, embryo with maxillar-prothoracic defect resulting from 

 KCN treatment in early stage (unbroken lines), superimposed on early embryo fixed 2 hours 

 after KCN treatment (dotted lines) with susceptibility, as indicated by injury, decreasing 

 from inner to outer elliptical lines; D, later embryo, showing partial duplication by KCN 

 treatment, complete in thoracic region and extending anteriorly into the head and posteriorly 

 through the thorax; E, complete duplication by cyanide treatment (from Brauer, 1938). 



the posterior region is supposed to block the movement of this substance; 

 but it also breaks the egg cortex, and a wound stimulus must result and 

 extend anteriorly from what is essentially a level of section. This may ob- 

 hterate more or less completely the anteroposterior gradient in the em- 

 bryonic region. With incomplete ligature continuity of the cortex is not 



