48 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



it even after the work of Heroic! and von Siebold." In order 

 to increase the number of Bombyx eggs that develop without 

 fertilization, Tichomiroff used a method of which the breeders 

 avail themselves in order to accelerate the development of 

 fertilized eggs. Certain kinds of silkworms lay their eggs in 

 the summer and these eggs begin to develop at once; but 

 during the winter the development ceases, and the caterpillars 

 do not hatch till the spring. Now it appears that it is cus- 

 tomary among the breeders to hasten the development of the 

 fertilized eggs by special "stimuli," so that the caterpillars 

 hatch out in the same summer in which the eggs are laid. 

 Tichomiroff applied the same methods to unfertilized eggs. 



The experiments consisted in stimulating eggs mechanically and 

 chemically in the same way as is done in order to obtain caterpillars 

 in the same summer from fertilized eggs which normally only develop 

 to a certain stage in summer. I plunged thirty-six unfertilized eggs 

 into concentrated sulphuric acid and left them there two minutes 

 (afterward the eggs were scrupulously washed). Thirteen of these 

 eggs began to change color on the fourteenth day. On the sixteenth 

 day an embryo could be perceived in these eggs. Both the embryo and 

 the serous envelope consisting of magnificent pigment cells appeared 

 quite normal. 



Sixteen other eggs were rubbed quite lightly with a brush. Up till 

 now (after one week [?]) the result has remained negative: not a 

 single egg has developed. A third batch of ninety-nine eggs were 

 brushed hard. On the fourth day the color change characteristic 

 of developing eggs was observed in six of these eggs. Not a single 

 parthenogenetically developing egg was observed among all the 

 unfertilized eggs which remained unstimulated. 



The breeders' experience that the immersion of eggs in 

 concentrated sulphuric acid, or brushing them, accelerates 

 development, is hard to explain. Both rubbing the eggs with 

 a brush and plunging them into sulphuric acid may serve, 

 perhaps, to injure or alter the skin of the egg, whereby it 

 becomes more permeable to oxygen. We shall see later that 



