REPRODUCTION AND SEX 503 



addition of certain chemical reagents to the blood or to the expressed 

 extracts of various kinds of organisms has for its final result a 

 certain colour for the male and another colour for the female. 

 In short, the sex can be told from the colour in the test-tube con- 

 taining the blood, or extract, or even sap. Now the difficulty has 

 been that while some experimenters, such as Manoilov and his 

 collaborators, are extraordinarily successful in applying this test 

 for sex, others get conspicuously discrepant results. Thus half a 

 dozen determinations may prove quite correct, while in the next 

 half-dozen three are right and three are wrong. 



A recent investigation by Professor Oscar Riddle and Dr. Warren 

 H. Reinhart has led to a suggestion which seems to us very shrewd. 

 The suggestion is that the colour difference is primarily an index of 

 the rate or intensity of the metabolism. Thus blood from younger 

 birds, with a high basal metabolism (i.e. routine of essential vital 



Fig. 73. 



The Pigmy Male of the Paper-nautilus [Argonauta argo). It differs very 

 markedly from the female not only in being very small, but in having 

 no shell. The figure shows one of the arms transformed ("hectocotylised") 

 as a vehicle for the sperm-packets or spermatophores . 



processes), gives a lighter colour than blood from older birds. 

 Aqueous extracts of active tissues (muscle, heart, gizzard) in doves 

 yield a colour lighter than that given by tissues presumably less 

 active, such as those of the liver. The glands of the bird's oviduct 

 jdeld a lighter colour when actively secreting, and a deeper colour 

 the further they are removed from active functioning. Similarly 

 extracts of whole embryos give the lightest colour when prepared 

 from freshly killed embryos; but decidedly darker when prepared 

 from embryos which have been dead for one to three days. Thus the 

 reason for the discrepancies in previous experiments, in which we 

 have shared, may be that the physiological state, in particular the 

 metabolic intensity, varies notably from one individual to another 

 and at different ages and seasons. 



This fits in well with the metabolic theory of sex first stated 

 by us in 1889, in The Evolution of Sex. According to this 

 theory, the ratio of Anabolism (constructive processes) to Kata- 

 bolism (down-breaking processes) is always relatively greater in the 

 females. In the male constitution there is a relative predominance 



