254 THE UNFERTILISED EGG AS A [pt. iii 



conditions the first egg laid nearly always gives rise to a male and the 

 second to a female. 



In Fig. 14 the line marked "developmental energy" implies that 

 a higher percentage of the male eggs hatch successfully than of the 

 female eggs. The data for length of life show the same curve. The 

 smaller eggs of both clutch and season are the eggs which give 

 positive results in strength and vigour tests, and the larger eggs are 

 those which are liable to display weakness. These facts are in entire 

 accord with the higher metabolic level which Riddle associates with 

 the small male eggs. It is interesting to note that Lawrence & 

 Riddle found consistently higher values for total fat and total phos- 

 phorus in the blood of female fowls than in that of male fowls, from 

 which they concluded that the metabolic differences between male 

 and female germs persist in the adult, and all these facts are in agree- 

 ment with the work of Goerttler and Baker on human and Smith on 

 crustacean blood-fat, and of Benedict & Emmes on sex differences 

 in basal metabolism. But for further discussion of the metabolic 

 theory of sex, the papers of Riddle must be consulted. Interesting 

 data on the hatchability, vigour, etc., of rotifer eggs are contained 

 in the paper of Jennings & Lynch, but these authors made no 

 chemical experiments. 



To say, as Riddle does, that there are, as it were, two kinds of eggs 

 in some species, one male-producing, and the other female-producing, 

 may either be taken to mean that there are quantitative differences 

 between them or that their constituent substances are qualitatively 

 chemically different, or, thirdly, that the same substances in the same 

 quantities are differently distributed spatially and temporally. As will 

 be seen later in connection with the lipoids of mammalian egg-cells, 

 the second view finds supporters, and some such opinion is held 

 by Russo. Faure-Fremiet, in the course of his work on the egg of 

 Ascaris megalocephala, to which he applied every conceivable method, 

 examined a very large number of individual eggs in order to find 

 whether they separated at all chemically into two types. His method 

 was to centrifuge them separately, much as McClendon had done 

 with the frog's egg, and then to measure in mm. the thickness of 

 {a) the mitochondria layer, and {b) the fatty layer. Fig. 15 {a) taken 

 from his paper shows the frequency polygon which he constructed 

 on the basis of these results, the ordinate giving the number of eggs 

 measured, and the abscissa the thickness of the mitochondrial layer. 



