1 6 VERNON L. KELLOGG. 



There is also to be noted a difference among races in the propor- 

 tion of unfertilized eggs which begin to develop. Among a 

 dozen races in our rearing rooms, one (a vigorous white-cocoon 

 race called Bagdad) is strongly inclined to normal parthenogene- 

 sis, from twenty-five to seventy-five per centum, even in a few 

 cases ninety-five per centum, of the eggs in unfertilized lots be- 

 ginning to develop. The more usual proportion, however, i. e., 

 that shown by the other races, is, as already noted, less than ten 

 per centum. So much for normal parthenogenesis in the species. 



In 1885 Tichomiroff discovered that by bathing the unferti- 

 lized eggs with concentrated sulphuric acid, or by rubbing them 

 gently, he could induce a considerably larger per centum than the 

 normal to begin development. He repeated his experiments, 

 confirming and extending his results, in 1902. By histologic 

 examination of the eggs he learned that the artificially stimulated 

 eggs which develop do so in a somewhat abnormal manner. 

 Tichomiroff held the stimulus to development to be neither the 

 action of specific ions, osmotic pressure nor catalysis. He be- 

 lieves that the eggs respond by segmentation to any appropriate 

 excitation, "whatever the nature of this excitation." 



Verson, in 1899, used electricity as a stimulus, and found that 

 the development thus initiated ceased at a point about corres- 

 ponding with that reached by a fertilized egg on the third day 

 after oviposition. 



Quajat (1905) submitted unfertilized eggs to the action of 

 oxygen, high temperatures, sulphuric acid, hydrochloric acid, 

 carbon dioxide, and electricity. His account of the experiments 

 indicates that he was able to stimulate development by several of 

 these agents, but he gives no data to show the proportion of 

 developing eggs in the various treated lots. No larva issued, 

 but by an examination of the eggs he found that several embryos 

 had practically completed their development and growth. 



My own experiments include the treatment of something over 

 a hundred lots of unfertilized eggs (a "lot" is all the eggs laid 

 by a single female, averaging from 100 to 350 in number), and 

 of several lots of fertilized eggs (to serve as controls to indicate 

 possible injury to the eggs from the reagents used). The stimuli 

 or agents used were dry air (obtained by drawing air through vessels 



