590 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1916. 



nized this new publication by awarding to the memoir on the Cerceris 

 a prize in experimental physiology. 



One of the best examples of the application of the experimental 

 method to the biology of insects is presented by Fabre's researches on 

 the laying of eggs by the species Osmia. The greater part of these 

 solitary bees build their cells in cavities where most convenient, in a 

 Helix shell, old gallery of an Anthophora, hollow stem of reeds or 

 brambles, etc. When they lay their eggs in hollow twigs the cells 

 are arranged in series, the largest at the bottom with the eggs first 

 laid, the last at the top, newer and smaller in size. Now those born 

 at the top are males, which emerge first, and the large earlier cells in 

 turn yield females. Can the bee have the instinct for placing in each 

 cell an egg of a desired sex ? Or, rather, will the sex of the egg be 

 determined by the food of honey and of pollen, which is less in the 

 male than in the female cells? By some simple experiments and 

 conclusions reached in his meager laboratory, Fabre proved without 

 contradiction the truth of the second hypothesis. He placed the eggs 

 of Osmia in a reed, and at the hatching time he introduced the foods, 

 putting a large supply in the small cells and a small supply in the 

 large cells. The result was always the same, except that the large 

 cells jdelded small females and the small cells, now well provisioned, 

 gave large males. In a larger reed the Osmia built with more irregu- 

 larity, but always placed a male egg in the small cells, a female egg 

 in the large cells ; and if it was compelled to divide its layings among 

 narrow shells where it was impossible to arrange large cells, it laid 

 only male eggs. From such a divided laying of 26 eggs Fabre ob- 

 tained 25 males and only 1 female. Therefore the egg which comes 

 from the ovaries does not determine the sex; but it acquires its sex 

 in traversing the genital paths, and the female possesses the instinct 

 of placing in each cell an egg of the sex desired. It may be said that 

 the Osmia has knowledge of the sex of the egg that it lays and that 

 it can produce this sex at will. This is one of the most beautiful dis- 

 coveries of Fabre and is due entirely to the application of the experi- 

 mental method. Without doubt the reason for the phenomenon 

 remains unknown, and one is lost in hypotheses to establish it; but 

 it is demanded that important works penetrate the domain of the 

 unknown until mystery totally disappears. 



To scrutinize and to follow in their enchantment the mysterious 

 habits of insects, it does not suffice to be an ingenious experimenter ; 

 there must be a keen observation, a patience that can not be discour- 

 aged and an extraordinary intuitive power. Fabre had these quali- 

 ties up to the point of genius and gave brilliant proof of it in his 

 studies on the blister beetles of the genera Sitaris and Meloe. All 

 that was known about the development of these insects, the so-called 

 lice of the solitary bees, for which the genus Triungulinus had been 



