468 



NATURE 



[February 14, 1918 



cumulative efficiency. That our people markedly 

 lack this intuitive mathematical faculty is too pain- 

 fully in evidence. A great opportunity is opening 

 out before us to correct this defect. Are we going 

 to make the attempt? Risk there will, of course, 

 always be, but in this case the risk of standing 

 still seems to be far greater than the risk, incident 

 upon the compulsory adoption of the metric system. 



A. F. B. 



CONTROL OF SEX IN PIGEONS.' 

 "T^HE late Prof. Whitman, of Chicago, was the 

 -*- first to show the remarkable suitability of 

 wild pigeons for the analysis of the sex-problem. 

 He found, for instance, that generic crosses 

 (Columba and Turtur), when not permitted to lay 

 many eggs, produce mostly or only males ; that 

 such pairs, when made to lay many eggs (crowded 

 reproduction), produce males predominantly from 

 their earlier stronger eggs,, and predominantly or 

 only females from the later eggs laid under stress 

 of overwork ; and that from eggs of pure wild 

 species the first egg of the pair or clutch more 

 often hatches a male, while the second egg of the 

 pair more often produces a female. Dr. Oscar 

 Riddle has followed up Prof. Whitman's work 

 with very important results, bearing not only on 

 the theory of sex, but also on possible practical 

 control. 



It seems certain that there are two kinds of 

 eggs in the pigeon's ovary. The male-producing 

 egg of the spring stores less material than the 

 female-producing egg of the autumn. The male- 

 producing egg of the clutch stores less material 

 than does its female-producing fellow. The eggs 

 of old females store more material and yield a 

 higher percentage of females than do the eggs 

 of birds not old. During the season successive 

 clutches present higher and higher storage, and 

 the eggs of the low-storage period give rise (in 

 the generic cross) to males, and those of the high- 

 storage period produce females. 



Increase in storage capacity means decrease in 

 oxidising capacity — a lowered metabolism ; and 

 the fundamental difference between the female- 

 producing ovum and the male-producing ovum is 

 a difference in the level of metabolism. Though 

 there are a few discrepant results, it may be said 

 that femaleness in the egg is associated with low 

 metabolism, lower percentage of water, and a 

 higher total of fat and phosphorus, or of phos- 

 phatides ; and conversely for maleness. The less 

 hydrated state of the colloids will favour increased 

 storage, while a more hydrated state will favour a 

 higher rate of oxidising metabolism. Analysis of 

 the blood and constitutional features of adult birds 

 gives some indication that the metabolic differences 

 of male and female germs persist in the male and 

 female adults. A calorimetric determination of 

 the energy-value of hundreds of eggs confirmed 

 the reality of what may be called metabolic 

 dimorphism, agreeing with the conclusions reached 

 from studies on the weights of yolks and on yolk 



1 " The Control of the Sex Ratio. " By O. Riddle. Journ. Washington 

 Acad. Sci.. vii. (1917), pp. 319-56. 



analysis, and strikingly consistent with the breed- 

 ing data. "We could say, if we wished to make 

 merry with our colleagues, the cytologists, that 

 we here get closest to the facts of sex when we 

 burn our chromosomes." 



Some of the incidental corroborations of Dr. 

 Riddle's thesis are very interesting. Thus females 

 hatched from eggs laid early in the season tend to 

 be more masculine in their sex-behaviour than 

 their own full sisters hatched later in the season. 

 " Several grades of females can be thus seriated 

 according to the season of hatching." Again, the 

 female hatched from the first egg of a clutch is, 

 in a great majority of cases, more masculine than 

 her sister hatched from the second of the clutch. 

 Another sidelight may be found in the frequency 

 of a persistence of the right ovary in birds hatched 

 from eggs which are otherwise known to be most 

 feminine. 



Numerous facts converge to the conclusion that 

 " sex and characteristics other than sex, such as 

 fertility and developmental energy, not only bear 

 initial relations to the order of the egg in the clutch, 

 but that sex and these other characteristics are 

 progressively modified under stress of reproductive 

 overwork, until at the extreme end of the season 

 certain aspects of femininity are abnormally or un- 

 usually accentuated. In the light of these facts 

 sex reveals itself as a quantitative modifiable 

 character," associated with modifiable metabolic 

 levels. 



Dr. Riddle's view of sex, based on experimental 

 results, is akin to the biological interpretation ex- 

 pounded by Geddes and Thomson in "The Evolu- 

 tion of Sex " (1889), that the fundamental dif- 

 ference between maleness and femaleness is a 

 difference in the ratio, of katabolic to anabolic pro- 

 cesses, and that the determination of sex is to be 

 looked for in factors affecting the rate and the 

 nature of metabolic processes in the ^erm-cells or 

 in the early stages of development. Dr. Riddle 

 partially recognises the anticipation : " A general 

 classification of male and female adult animals on 

 the basis of a higher metabolism for the one and 

 a lower for the other was indeed made by 

 Geddes and Thomson many years ago. It now 

 seems beyond question that this conclusion of these 

 authors is a correct and important one." 



Dr. Riddle's physiological view of sex is in har- 

 mony with many experimental results reached by 

 other investigators, as may be illustrated by refer- 

 ence to Baltzer's beautiful experiments on the 

 worm Bonellia, where there is striking dimorphism 

 between the large female and the pigmy male. 

 The newly hatched larvae are capable of becom- 

 ing either. If they happen to become attached 

 to the proboscis of an adult female they become 

 males ; if they settle into the sand and mud they 

 undergo, quite slowly, further development into 

 females (almost, exclusively). If the free- 

 swimming, indifferent larvae are artificially helped 

 to a connection with the proboscis of an adult 

 female, and then removed at progressively longer 

 periods, the significant result is the production of 

 practically all stages of hermaphroditism. Those 



NO. 2520, VOL. 100] 



