Mosaic Development in Ascidian Eggs. 201 



The statements of Driesch and Crampton are even more posi- 

 tive and explicit that whole larvae are formed from any one or 

 more of the first four blastomeres. Driesch (p. 405 in sum- 

 marizing his results uses, in part, the very words of his conclusions 

 regarding the value of the cleavage cells in the echinoderm egg: 

 "Aus isolirt iiberlebenden Blastomeren des Ascidieneies ent- 

 wickelt sich nicht ein halber (resp. viertel, drei viertel) rechter oder 

 linker (resp. vorderer odef hinterer) Embryo, sondern stets ein 

 ganzer von halber Grosse, dem allerdings (meist) gewisse Organe 

 von minderen Bedeutung (Otolith, ein Haftorgan fehlen." 

 Crampton neither figures nor describes the larvae obtained from 

 isolated blastomeres of Molgu'a, bu" he savs, p. 55, "Enough of 

 the later developrnent has been ascertained o prove that a larva 

 arises wh ch resembles the normal larva, except as regards its 

 smaller size and certain minor defects. My results, therefoie, 

 are entirely confirmato y of those of Driesch upon Phallusia." 



Chabry first discovered that larvae from one of the first two 

 blastomeres were superficially like normal larvae in that they had 

 head and tail, notochord, neural plate and sense spots, but he 

 showed that they also lacked the organs distinctive of the missing 

 side, viz: one papilla, one or more sense spots and one atrial 

 invagination. It s surprising therefore that neither Driesch nor 

 Crampton undertook to prove that the larvae obtained by them 

 from one of the first two blastomeres were really complete. One 

 looks in vain in their papers for any evidence that the organs 

 characteristic of that side which would have developed from the 

 dead half (muscles, mesenchyme, papilla, atrial invagination) are 

 present in the surviving half. 



Chabry further showed that the type of embryo derived from 

 the anterior or posterior two-quarters of the egg was very unlike 

 that derived from the right or left two-quarters, while the one- 

 quarter embryos were still more unlike the normal; n each of these 

 cases he found that the development was strictly partial, only 

 those parts arising from a blastomere which would develop from 

 it in the normal embryo. In the face of these conclusions of 

 Chabry's neither Driesch nor Crampton advance any evidence in 

 favor of their claim that the anterior and posterior quadrants of 

 the egg as well as the right or left may give rise to a larva. Cha- 

 bry's figures and descriptions show plainly what my work proves 

 that nothing even remotely resembling a normal larva is ever pro- 



