EMBRYOLOGY. 1 



Epigenesis or Evolution?- — One part of this paper is devoted to 

 the results of certain experiments upon the action of light upon the 

 cleavage of eggs. These show that the eggs of EehinvA 



latus, Planorbis carinatusf and Rana esctdenta undergo cleavage and 

 the early stages of organ formation equally well in darkness, white 

 light or colored light. Light then has no effect upon the early stages 

 of development, though others have shown that the presence or absence 

 as well as the color of light does have an effect upon the later stages 

 of differentiation of embryos. 



The main portion of the paper, however, contains the most interest- 

 ing results : that from one of the first two blastomeres of the egg of 

 Echinus in In- >''■'" r'-nlnfus, and the same is true of a specie.- of Spine- 

 rechinus, a complete pluteus of normal form but of half the normal 

 size may be reared ! 



Owing to the importance of these experiments as bearing upon the 

 value of the blastomeres upon the question of early potential repara- 

 tion of organs within the egg, thai is, upon the question of evolution as 

 opposed to epigenesis, it will he necessary to give here a brief account 

 of the author's methods, from which the chance of error may be 

 deduced. 



When the first cleavage furrow has come in, 50-100 eggs are shaken 

 vigorously for five minutes, with little water in a test tube 4 cm. long 

 and 0'6 cm. wide, then quickly poured into clean sea water and exam- 

 ined. If the right moment has been taken, neither too soon nor too 

 late, some of the blastomeres will be found not only isolated but still 

 alive, others of course dead, or not separated from their fellows as the 

 egg membrane does not always burst open. There is also great varia- 

 tions in the resistance offered by eggs of different individuals— some 

 may need to be shaken several times. 



The best isolated cells are removed and placed two or three 

 together in sea water in solid watch glasses covered, and with a hang- 

 ing drop on the cover to diminish evaporation and concentration of 



observed from time to time without removal. 



