1896.] Embryology. 81 



The author maintains that the few dwarf bastards that were like the 

 male parent came from nonnucleated pieces of Sphaereehinus penetrated 

 by a sperm of Echinus. This, however, is an indirect result of all the 

 above facts, It should also be borne in mind that Morgan, as cited 

 above, was not successful in obtaining a cross fertilization of enucleated 

 fragments and that both Morgan and Seeliger 10 find the bastards 

 between Sphaerechinus and Echinus so variable that Boveri's experi- 

 ment in which they appeared as exact intermediate forms seem an 

 exception and hence may be withdrawn from the evidence. 



Hans Driesch starting from the standpoint that it has been proved 

 that isolated cleavage cells may produce an entire organism seeks to 

 find where the limits of this power appear in the subsequent stages of 

 development. 



He cut blastulse of Sphaerechinus into pieces, chopping at random 

 with scissors in a dish full of gastrulae. When isolated the larger pieces 

 formed gastrulae or later larvae, in most cases. 



When the gastrulae of the starfish, Asterias glacialis were cut in the 

 same way some lost the inner end of the gastric invagination together 

 with much ectoderm. After healing over the wound the new end of 

 the gastric invagination enlarged and sprouted out the two ccelomic 

 pouches that would have, normally, been formed from the part that was 

 cut away : the power to form coelemic pouches was thus vicariously 

 assumed by a part that would normally have produced part of the 

 definitive digestive tract. Such larvae go on to form a normally three 

 chambered digestive tract from what would, normally, have formed but 

 part of the whole. 



The author concludes that the powers of the ectoderm or of the ento. 

 derm cells are as yet not restricted as to what organs or parts they may 

 form in their proper germ layer. 



When larva; with the mesenchyme were cut and a piece with only 

 ectodermal cells was isolated in 53 cut of 99 cases no gastrulation took 

 place but only a healing of the wound though life and activity might 

 last for a week. 



In a few cases when the digestive tube was removed from such larvae 

 it did not grow but died after a few days. In 19 cases where the end 

 of the gastric invagination was removed after it had enlarged and 

 sprouted out the coelemic pouches 17 did not form new ccelemic pouches. 

 In like manner when a cut happened to remove the skeleton of one side 

 it was not formed again. 



We thus soon come to a state in which the primitive tendency of 

 cells to replace others in organ formation seems lost. 



10 See American Naturalist, March, 1895. 6 



