78 The American Naturalist. [January, 



Chun's work was done 18 years ago and was, as stated in a letter to 

 Eoux ; 6 as follows. 



When the first two cells of the eggs of the lobate Ctenophore, Bolina 

 hydatina were separated by shaking each developed as a halflarva with 

 four ribs or bands of locomoter appendages instead of the normal eight, 

 two entodermal sacs in place of four and only one tentacle in place of 



The first cleavage plane coincides with the sagittal plane of the adult 

 and the second with the transverse. 



Half-larvse with 4 ribs, 4 meridional vessels one tentacle and an 

 oblique stomach may become sexually mature, developing eggs and sperm 

 under the two subventral meridional vessels! 



The missing half is regenerated during the postembryonic metamor- 



Driesch and Morgan worked on another Ctenophore, a nontentacul- 

 ated form, Bero'e ovata and finding it impossible to employ the shaking 

 method cut the eggs with special scissors. 



Isolated cells of the two cell stage develop into blastulae, gastrulse 

 and finally into larva that are most remarkable in being neither com- 

 plete nor halflarva? but larva? deficient in certain organs. 



The cleavage of such an isolated cell is much as it would be if still 

 associated with the other cell in a normal egg : it is a half cleavage as 

 compared with a normal egg. This, however, is not true of the cells 

 that form the ectoderm but only of the peculiar group of cells forming 

 the entoderm. The former cells grow over the half-group of entoderm 

 ceils and form a larva that is complete on the surface. 



The final larva is abnormal in usually having only 4 ribs instead of 

 8 and 3 pouches instead of 4. 



A second series of experiments seems to throw much light upon the 

 influence of protoplasm versus nucleus in the causation of such imper- 

 fect development. 



When a piece of the protoplasm of an entire egg is cut off, the egg, 

 deprived of some protoplasm but with it nucleus intact, as far as known, 

 develops into a larva that may be deficient in just the same way as is a 

 larva reared from one of the isolated cells. 



In another paper 7 Morgan finds the shaking method will not succeed 

 with the blastulae of Sphserechinus as they die when shaken. In 

 Echinus, however, both blastulae and gastrulae may be shaken into 

 pieces that will live. 



6 rdem, Oct. 25.95, pps. 444-447. 



7 Idem, pps. 257-266. 



