32 T. ART. 1. FUJTTA : OX THE FORMATION 



mesomere." By my investigation given above as well as by those 

 of others it is known that this generation is the most active in 

 its growth, at least before the establishment of a bilateral sym- 

 metry. They ought to have given rise to daughter-cells before 

 the true mesoderm "Kleine Zelle???," was first perceived by the 

 author. By a careful study, however, T have at last found that 

 his description and figures do not harmonize. In his description 

 not a' word is said as to the fate of his anterior blastomeres A 

 and B i. e. really the posterior C and D of authoi'S. But we 

 can ascertain from his Fig. 20 that these cells segment almost 

 :it the same time. In sliort, according to his paper we nnist 

 finally arrive at the very embarrassing conclusion that he has put 

 three totally different kinds of cells under one and the same name 

 of "the mesoderm" viz., (1) the descendants of the second ectomere- 

 cells or according to the author 2e and Id (Fig. 10), and (2) 

 the descendants of the entomere C or according to the autho]" rt>, 

 in addition to (3) the descendants of the proper mesomere, which 

 seems to have been entirely overlooked by the author. Yet these 

 c(dls, as they represent the ectomere-, the entomere-, nnd the meso- 

 mei-e-cells ought not of course to be confounded. This and some 

 other conclusions of the author, which I can not help considering as 

 too hasty are derived from his assumption of the homology 

 existing in the formation of the original mesomere-cells in the 

 species in question and in Polyclads. The fact is clearly seen 

 in his own tei-m — "Der Ursprung und die Lage dieser 2 Zelle 

 m und Wx stimmt so aufiallend mit denjenigen bei Polycladen 



überein, " 



In the same year a paper entitled " The Early Development 

 of Planorl)is " was made public by Holmes. By a careful study 

 of this author new liglit has been thrown on many points, 



