88 INHERITANCE IN SILKWORMS, I 



remain yellow and, after a while, collapse. Eggs which begin to develop either 

 persist in spherical shape, which indicates persisting life, or collapse, which 

 means death. The development of unfertilized eggs rarely proceeds, without 

 artificial stimulus, beyond a very early embryonic stage. In fully 500 clutches 

 or broods of unfertilized eggs (from confined females from isolated cocoons) 

 under observation, not a single egg gave up its larva, although an average of 

 about seven or eight per centum of the eggs began to develop. 



Although this parthenogenetic development always ceases and the embryo 

 dies before reaching hatching stage, much difference in vitality or duration of 

 life of the egg (strictly, embryo) is noticeable. Some of the developing eggs 

 collapse within a few days, some in a few weeks, while a few persist for several 

 months. (The normal egg stage, i. e., time from egg laying to hatching of 

 larvae in the silkworm univoltin races, is about nine months.) There is also to 

 be noted a difference among races in the proportion 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 parthenogenesis, 

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

 centum, of the eggs in unfertilized lots beginning to develop. The more usual 

 proportion, however, i. e., that shown by the other rapes, 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 unfertilized eggs with 

 concentrated sulphuric acid, or by rubbing them gently, he could induce a con- 

 siderably 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 believes that the eggs respond by segmentation to any appropriate 

 excitation, "whatever the nature of this excitation." 



Version, in 1899, used electricity as a stimulus, and found that the develop- 

 ment thus initiated ceased at a point about corresponding 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 develop- 

 ment 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 exami- 

 nation 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 

 of calcium chloride and then of concentrated sulphuric acid), high temperature, 

 sunlight, friction, sulphuric acid, hydrochloric acid, glacial phosphoric acid, 

 glacial acetic acid, absolute alcohol, potassium hydroxide, ammonia, and lime 



