154 Edivin G. Cotiklin. 



after cleavage begins it can scarcely be doubted that their poten- 

 cies are also the same. Hundreds of experiments involving many 

 thousands of eggs were made upon the various cleavage stages. 

 The methods of experimenting which I employed were essentially 

 like those used by Driesch and Crampton, viz: the eggs in the 

 2-cell, 4-cell, 8-cell or later stages were strongly spurted with a 

 pipette, or were shaken in a vial, and thereby some of the blasto- 

 meres were frequently injured while others were uninjured and 

 continued to develop. The injured blastomeres were rarely 

 killed, as was shown by the fact that they remained transparent 

 and entire for a day or more, whereas dead cells soon become 

 opaque and disintegrate. These injured cells never again divide 

 and sections show that their nuclei are frequently broken and 

 their chromosomes scattered. Cells are more likely to be injured 

 during nuclear division than during rest. The fact that these 

 injured cells never again divide though they remain whole within 

 the chorion and preserve their characteristic color and structure 

 makes it possible to determine at all stages just what cell or cells 

 have been injured. Whether or not the presence of these injured 

 cells within the chorion may influence the development of the 

 uninjured cells will be considered later. Attempts to completely 

 separate individual blastomeres by the use of Herbst's calcium- 

 free sea water were not successful, probably owing to the presence 

 .of the chorion and to the close union between the blastomeres. 



In addition to this method of experimentation which yielded 

 hundreds and thousands of eggs in which one or more of the blasto- 

 meres had been injured I also cut eggs and embryos in two with 

 knives made from small needles. In no single instance was I able 

 to get fragments of unsegmented eggs to develop; in the gastrula 

 stages I was more successful, being able to cut gastrula in two 

 in the manner described by Driesch ('03) and observe the 

 subsequent development. 



I have not attempted to repeat the various mgenious methods 

 of injuring blastomeres which were devised and employed by 

 Chabry, since they are necessarily slow and difficult of application 

 and yield but a small number of injured eggs, whereas by simply 

 spurting or shaking the eggs one may injure blastomeres in an 

 enormous number of eggs which can then be sorted out and classi- 

 fied according to the character of the injures furthermore the ease 

 and certainty with which the identity of injured blastomeres of 



