PROBLEMS OF ORGANIZATION 193 



Stance or material passed from the periblast during the course of early 

 cleavages. The postulate holds better for Fundulus where complete 

 embryos are not obtained until after the 32-cell stage as compared with 

 Carassius where similar formations are obtained at the 8-cell stage.* 

 Tung, Chang, and Tung consider that the passage of necessary materials 

 is accomplished earlier in Carassius because of the small proportion of 

 yolk present. Lewis and Roosen-Runge ('42) have studied cinemato- 

 graphically the movements in fish eggs (Danio) and find that there is 

 an early movement originating in the vegetal region of the tgg after 

 fertilization which up to now has not been considered a general reac- 

 tion of the differentiating organism. These movements are quite pro- 

 nounced, moving in a vortex from the vegetal pole towards the center 

 of the egg, resulting in rearrangements of materials at fertilization and 

 in migration of cortical parts definitely through the yolk substance to 

 form a layer, not uniform in its constituency, on top of the yolk between 

 the yolk and the blastoderm. This is a clear indication of the fact that 

 materials in early eggs still have certain visible effects which later are 

 to be correlated with the prospective parts of the developing organism. 



The observations of Lewis and Roosen-Runge have their counter- 

 part in the study of rhythmical contractions observed by Yamamoto in 

 a series of papers extending from 1931 to 1938. All of his studies have 

 to do with the early rhythmical movements which are found during the 

 early stages of the egg before segmentation. The significance of these 

 is yet to be interpreted. They may be osmotic in nature but the resultant 

 end point of such a reaction will bring about changes within the egg 

 and cause material dispositions which have a bearing on later organic 

 localizations. 



Morphogenetic movements have been plotted in various groups of 

 vertebrates, first in the amphibian by Vogt ('25, '29) in his classic 

 monographs on both the urodele and anuran, then on fishes by Pasteels 

 ('33' '34) ^"d by Oppenheimer ('35, '36b) and later Luther ('36), by 

 Pasteels ('36) for the chick now supplemented by Spratt's ('46) studies 

 with carbon particles, and in mammals by Vanderbroek (unpublished). 

 The vital staining experiments analyze to a large degree the paths fol- 

 lowed by cells and by cellular aggregates during the course of their 

 subsequent assumption of position in the embryo. 



It gives, however, no index of the effective agents which act upon the 



* During the summer of 1948 Dr. T. C. Tung was able to secure complete embryos 

 in Fundulus after isolating the embryonic blastodisc at the 4-cell stage (personal com- 

 munication). 



