200 Edwni G. Conkltn. 



However, it is quite evident from the observations ot Van Beneden 

 and Julin, Chabry, Castle and many others that something more 

 than a mere invagination is necessary to constitute a normal 

 gastrula. The ascidian gastrula is bilaterally symmetrical and 

 its anterior and posterior portions are very unlike; furthermore 

 all the principal organs of the larva are here represented by cells 

 of peculiar structure and localization. In order to determine 

 whether a gastrula is normal or not all of these features have to be 

 considered, and this Driesch has not done. 



L 



arva. 



It is somewhat surprising that doubt should have been expressed 

 as to whether Chabry obtained half embryos or whole embryos of 

 half size from one-half of the ascidian egg. He again and again 

 declares that lesion of a single cell up to the i6-cell and probably 

 up to the 32-cell stage always causes a "hemiterie," or monster. 

 (Chabry, pp. 246, 249, 250, 257, 258, 261, etc.) He even enters into 

 a calculation of the number of kinds of monsters which may be 

 produced by injuries to the cleavage cells. He says that if at the 

 8-cell stage each cell is capable of four different kinds of modifica- 

 tion (certainly less than the reality), the number of modalities of 

 this stage is 4^ ( = 65536) of which only one is normal. In this 

 way there arises that "admirable and infinite variety of monsters" 

 to which he repeatedly refers. He says expressly, p. 289, "De la 

 on tire aisement la conclusion (que je ne crois valable que pour 

 I'Ascidie et les animaux, dont les blastomeres sont differencies de 

 bonne heure), que chaque blastomere contient en puissance cer- 

 taines parties dont sa mort entraine la perte irremediable et que 

 les differentes parties de I'anmial sont preformees dans les differ- 

 entes parties de I'oeuf." Again on p. 299 he says, "On ne saurait 

 done conclure avec securite de I'oeuf d'Ascidie a celui des autres 

 animaux, mais, en ce qui concerne celui-ci, il est exact de dire 

 qu'il se comporte comme s'il contenait en puissance un seul adulte 

 determine et que chaque partie de I'oeuf contint une parrie de cet 

 adulte." This same conclusion is repeated again and again so 

 that as Barfurth ('93) and Driesch ('95) have said there can be no 

 question as to what Chabry believed that his observations and 

 experiments proved. 



