THE DETERMINATION OF SEX. 99 



observation is even more important. He discovered that there are large 

 and small eggs laid by the silk-worm moth, and that the caterpillars 

 emerging from the large eggs are, in the great majority of cases (88 

 to 95 per cent.), females, while those from the smaller eggs give a 

 corresponding majority of males (88 to 92 per cent.). It is there- 

 fore clear that the difference in size corresponds to a difference in the 

 sex of the embryos, and that with sufficient care it would be possible to 

 separate the two sorts of eggs so completely that all of one kind 

 would be females and of the other males. A similar result has been 

 obtained by Joseph in another moth, Ocneria dispar. Cuenot states 

 that he has been able to verify completely this statement of Joseph. 



How can we explain the apparent contradiction between the results 

 of Landois, Treat and Gentry, and those of Brocadello, Joseph and 

 Cuenot? It is probable that in all cases the facts recorded are correct. 

 Cuenot suggests that in the lots of caterpillars that were poorly 

 nourished there was a large mortality of the young females, so that of 

 those surviving there was a larger percentage of males. If we apply this 

 same view to the case in which abundant feeding gives rise to more 

 females we shall have to assume that here a larger percentage of males 

 are eliminated, but it is not at all evident why this should be the case. 

 Cuenot points out another possible source of error; namely, that in 

 selecting the caterpillars for the experiment the larger ones may have 

 been picked out to be given an abundant diet and the smaller ones for 

 a meager diet. If this had been done consciously, or unconsciously, 

 the results would not be due to the quality of the food, because the 

 young caterpillars that were large were already females (having come 

 from larger eggs), and those that were small were already males 

 (having come from small eggs). It is clear, therefore, that all the 

 early experiments must be repeated and the precaution taken to note 

 the number of caterpillars at the beginning and at the end of the 

 experiment, and the sex of those that die must, if possible, be deter- 

 mined. Care must also be taken that no selection of large and of 

 small individuals takes place. Since, however, it has been so clearly 

 shown by Brocadello and by Cuenot that large eggs become females 

 and small eggs males, it will be desirable in repeating the experiments 

 to take this fact into account, and to attempt to discover if the poten- 

 tialities of the large and of the small eggs can be changed by external 

 conditions. Here we have a new field for experimental work that will 

 yield results of great interest. The lines are now so definitely drawn, 

 and it is clearly so important to settle this question on as many forms 

 as possible, that it is much to be hoped that in the near future many 

 workers will turn their attention to this important subject. 



Cuenot 's experiments on certain flies, belonging to four different 

 genera, are of especial interest. In this group also it had been claimed 



