Reproduction and Development. 59 



workers ; but what may be the nature of the stimulus that 

 prompts the queen to withhold fertilization we at present do 

 not know. The difference between the fertile queen and 

 the unfertile worker seems to be entirely a matter of 

 nutrition. If all the queen-embryos should die, the 

 workers will tear down the partitions so as to throw three 

 ordinary worker-cells into one ; they will destroy two of the 

 embryos, and will feed the third on highly nutritious and 

 stimulating diet; with the result that the ovaries and 

 accessory parts are fully developed, and the grub that 

 would have become an infertile worker becomes a fertile 

 queen. And one of the most interesting points about this 

 change, thus wrought by a stimulating diet, is that not 

 only are the reproductive powers thus stimulated, but the 

 whole organism is modified. Size, general structure, sense- 

 organs, habits, instincts, and character are all changed 

 with the development of the power of laying eggs. The 

 organism is a connected whole, and you cannot modify one 

 part without deeply influencing all parts. This is the law 

 of correlated variation. 



Herr Yung has made some interesting experiments on 

 tadpoles. Under normal circumstances, the relation of 

 females to males is about 57 to 43. But when the tadpoles 

 were well fed on beef, the proportion of females to males 

 rose so as to become 78 to 22 ; and on the highly nutritious 

 flesh of frogs the proportion became 92 to 8. A highly 

 nutritious diet and plenty of it caused a very large pre- 

 ponderance of females. 



Mrs. Treat, in America, found that if caterpillars were 

 half-starved before entering upon the chrysalis state, the 

 proportion of males was much increased; while, if they 

 were supplied with abundant nutritious food, the proportion 

 of female insects was thereby largely increased. The same 

 law is said to hold good for mammals. Favourable vital 

 conditions are associated with the birth of females ; un- 

 favourable, with that of males. Herr Ploss attempts to 

 show that, among human folk, in hard times there are more 

 boys born ; in good times, more girls. 



