SEXUAL SELECTION. 205 



cayed wood, whilst the female probes the softer parts with her 

 far longer, much curved and pliant beak: and thus they mu- 

 tually aid eaeh other. In most cases, differences of structure 

 between the sexes are more or less directly connected with the 

 propagation of the species: thus a female, which has to nourish 

 a multitude of ova, requires more food than the male, and con- 

 sequently requires special means for procuring it. A male ani- 

 mal, which lives for a very short time, might lose its organs for 

 procuring food through disuse, without detriment; but he would 

 retain his locomotive organs in a perfect state, so that ha might 

 reach the female. The female, on the other hand, might safely 

 lose her organs for flying, swimming, or walking, if she gradu- 

 ally acquired habits which rendered such powers useless. 



We are, however, here concerned only with sexual selection. 

 This depends on the advantage which certain individuals have 

 over others of the same sex and species solely in respect o!: repro- 

 duction. When, as in the cases above mentioned, the two sexes 

 differ in structure in relation to different habits of life, they have 

 no doubt been modified through natural selection, and by in- 

 heritance limited to one and the same sex. So again the primary 

 sexual organs, and those for nourishing or protecting the young, 

 come under the same influence; for those individuals which gen- 

 erated or nourished their offspring best, would leave, oasteris 

 paribus, the greatest number to inherit their superiority; whilst 

 those which generated or nourished their offspring badly, would 

 leave but few to inherit their weaker powers. As the male has 

 to find the female, he requires organs of sense and locomotion, 

 but if these organs are necessary for the other purposes of life, 

 as is generally the case, they' will have been developed through 

 natural selection. When the male has found the female, he 

 sometimes absolutely requires prehensile organs to hold her; 

 thus Dr. Wallace informs me that the males of certain moths 

 cannot unite with the females if their tarsi or feet are broken. 

 The males of many oceanic crustaceans, when adult, have their 

 legs and antennae modified in an extraordinary manner for the 

 prehension of the female; hence we may suspect that it is be- 

 cause these animals are washed about by the waves of the open 

 sea, that they require these organs in order to propagate their 

 kind, and if so, their development has been the result of ordinary 

 or natural selection. Some animals extremely low in the scale 

 have been modified for this same purpose; thus the males of 

 certain parasitic worms, when fully grown, have the lower sur- 

 face of the terminal parts of their bodies roughened like a rasp, 

 and with this they coil round and permanently hold the females.* 



* M. Perrier advances this case ('Revue Sclentiflque,' Feb. 1, 1873, 

 p. 865) as one fatal to the belief in sexual selection, inasmuch as he 

 supposes that I attribute all the differences between the sexes to 



