144 PATTERNS AND PROBLEMS OF DEVELOPMENT 



Since the basal region of this egg consists largely of yolk, the apical region 

 of cytoplasm, and the rate of cleavage and morphogenesis is much higher 

 apically, this result is rather surprising. There can be little doubt that it, 

 like the reduction differential observed by Gersch in Paramecium (p. 92, 

 footnote 2), results from injury by the very toxic Janus green to the 

 apical region, and consequent retardation or absence of reduction there. 

 There is no evidence in this work of any attempt to determine whether 

 different concentrations of dye and dififerent staining periods would give 

 different results. ^^ 



Direct evidence of physiological differentials or regional specificities in 

 early stages of arthropod development appears to be lacking, except for 

 demonstration of differential suceptibility to cyanide in the insect Bruchus 

 quadrimacidatus (Coleoptera). In stages from egg-laying to 6| hours sus- 

 ceptibility becomes highest on the ventral surface, and the most suscepti- 

 ble area gradually becomes localized in the median ventral, presumptive 

 prothoracic-maxillary region. From 6^ to 12 hours ectodermal suscepti- 

 bility decreases from this region anteriorly through the head region and 

 posteriorly through the embryonic plate; from 12 to 16 hours it remains 

 essentially the same. The locus of highest susceptibility in the ventral 

 prothoracic region is the position of the "differentiation center" of Seidel 

 (pp. 515-21). The aggregations of nuclei at certain regions of the cortical 

 layer of the insect egg, their changes of position in some eggs, and the 

 progress of formation of cell boundaries about them from certain egg 

 regions indicate, of course, presence of physiological pattern of some 

 sort; but of what sort, these observations do not show. 



During the summer and autumn, 1940, suggestive data on differential 

 reduction of methylene blue and Janus green in the ovaries of the insect 

 Drosophila hydei have been obtained (Child, unpublished). The ovaries 

 consist of parallel series or strings of follicles in each of which the basal 

 cell becomes the egg, the other cells becoming accessory or nurse cells. 

 The apical pole of the egg is toward the apical ovarian pole, that is, the 

 pole where follicle development begins; and the ventral side of the egg is 

 toward the outer ovarian surface. If overstaining and differential injury 

 are avoided, dye reduction in low oxygen progresses basipetally in the 



^' These authors have investigated various aspects of cytoplasmic differentials and differ- 

 entiations in eggs and early stages of a considerable number of animals, with certain results of 

 interest and undoubted value; but in some respects the data presented appear inadequate as a 

 basis for the conclusions drawn and suggest the need of a considerably wider range of experi- 

 ments. See Ries und Gersch, 1Q37; Ries, 1937; Gersch und Ries, 1937; and their citations of 

 earlier papers. 



