378 The American Naturalist. [May, 



time of year, the latter part of the spawning season, some 

 similar abnormalities were found in eggs that had not been 

 operated upon at all. The various stages of abnormal growth 

 were hardened, stained and sectioned. The results of such 

 injury may be considered, first as relates to the uninjured and 

 then to the injured half of the two celled stage. 



The single cell by side of the injured one develops in many 

 cases into a half embryo, first a half blastula, a half gastrula 

 then a half embryo with medullary fold, archenteron, chorda, 

 mesoblast and metameres representing only half of the normal 

 condition of these organs. 



In the four-celled stage injury to both posterior cells some- 

 times resulted in formation of only anterior half of medullary 

 folds. Injury to three or to one of the cells resulted cither 

 in one-fourth blastula; or in the other cases three-fourths 

 embryos. Finally injury above or below the first horizontal 

 furrow gave rise to some cases of upper half blastuke. 



He concludes that as each of the first two cells may develop 

 up to stage of medullary folds without aid from the other, 

 there is marked self-differentiation and that the cleavage 

 planes separate the material qualitatively and thus determine 

 the subsequent position of the organs. The last experimeot 

 also indicates that the gastrula or embryo is a mosaic made 

 up of at least four vertical elements or independent parts. 



Turning now to the complex phenomena that take place 

 in the cell operated upon, regarded by Jtoux as dead, though 

 evidently this is scarcely justifiable from its subsequent history 

 we find three series of events taking place: 1st disintegration, 

 2nd reorganization, 3d post generation. 



In the first category are included, a vacuolation of the yolk, 

 the appearance of a net work within it in places and the for- 

 mation of peculiar bodies regarded as nuclei derived from the 

 original nucleus of the operated cell. Here again we must 

 not overlook the fact that some eggs found at this season do 

 not develop but have similar abnormal nuclei. Only about 

 one-third of the eggs operated upon and subsequently sec * 

 tioned present these phenomena of disintegration. 



