Iq8 Edwin G. ConkhfT. 



logical development ot this species and it was carried out with a 

 delicacy and precision of method which has never been surpassed. 

 Add to this the fact that the work was undertaken with clear 

 insight into the principal problems involved and at a time when 

 almost no other work of this sort had ever been done^ and its right 

 to rank as one of the great works in experimental embryology 

 seems assured. Considering these facts it is surprising that this 

 work should have received so little attention and that it should 

 have been so widely misunderstood or discredited. 



Chabry's extensive experiments deal with right and left half 

 embryos, anterior and posterior two-quarter embryos, and various 

 forms of three-quarter, one-quarter and two-quarter diagonal 

 embryos, and in all of these I find that my results are in the main 

 in accord with his. The points in which my work is more detailed 

 than his concern the presence and distribution of the various 

 ooplasmic substances and the more accurate study of some of the 

 later stages, made possible by the use of fixed and stained material. 

 That the substance of the mesodermal crescent was seen by Chabry 

 as early as the 32-cell stage is evident from his description of the 

 mesoderm cells, which in Ascidia aspersa are greenish (" verdatre") 

 in color and which he recognized when only three were present on 

 each side. Neither Driesch nor Crampton speak of having 

 observed any of these ooplasmic substances and neither of them 

 studied the later stages by means of fixed and stained material. 



I . Cleavage. 



Chabry showed that in rhythm of cleavage and in the size and 

 character of the daughter cells the isolated blastomeres of Ascidia 

 behave as if they were still part of the normal egg, while he 

 described in great detail the changes which take place in the facets 

 between cells. Crampton's conclusions are very similar; he 

 found that "an isolated blastomere of the Molgula egg segments 

 as if still forming a corresponding part of an entire embryo. The 

 cleavage phenomena are strictly partial, as regards the origin of 

 cells, the inclination of cleavage planes, and especially in respect 

 to the rhythm of segmentation." Driesch, on the other hand, 

 found in Phallusia that there was no fixed relation between the 



'See Roux, Ges. Abhand II, p. 958. 



