48 THE GENETIC AND THE OPERATIVE EVIDENCE 



called upon for a different explanation for other differences that dis- 

 tinguish the sexes? One example will suffice to bring out a curious 

 emotional (?) display that, elaborate as it is, has no apparent connec- 

 tion with mating (p. 269) : 



"The lapwing display, called by the natives its 'dance' or 'serious dance' — 

 by which they mean square dance — requires three birds for its performance, 

 and is, so far as I know, unique in this respect. The birds are so fond of it 

 that they indulge in it all the year round, and at frequent intervals during the 

 day, also on moonlight nights. If a person watches any two birds for some 

 time — for they live in pairs — he will see another lapwing, one of a neighboring 

 couple, rise up and fly to them, leaving his own mate to guard their chosen 

 ground ; and instead of resenting this visit as an unwarranted intrusion on their 

 domain, as they would certainly resent the approach of almost any other bird, 

 they welcome it with notes and signs of pleasure. Advancing to the visitor, 

 they place themselves behind it; then all three, keeping step, begin a rapid 

 march, uttering resonant drumming notes in time with their movements ; the 

 notes of the pair behind being emitted in a stream, like a drumroll, while the 

 leader utters loud single notes at regular intervals. The march ceases; the 

 leader elevates his wings and stands erect and motionless, still uttering loud 

 notes; while the other two, with puffed-out plumage and standing exactly 

 abreast, stoop forward and downward until the tips of their beaks touch the 

 ground, and sinking their rythmical voices to a murmur remain for some time 

 in this posture. The performance is then over and the visitor goes back to 

 his own ground and mate, to receive a visitor himself later on." 1 



Cunningham, who has brought together many interesting cases of 

 secondary sexual differences in his book on "Sexual Dimorphism in the 

 Animal Kingdom," attempts to show that the development of the 

 secondary sexual characters of the males are due directly to the use of 

 certain parts of the body during courtship — the use of the parts leading 

 to the enlargement and excessive growth of the parts. The effects 

 are believed by him to be inherited, and he tries, furthermore, to show the 

 way in which such acquired characters could be inherited. He makes 

 use of the modern idea of hormones — substances that are elaborated 

 in many organs of the body, whose effects are often most conspicuously 

 produced in other parts of the body. He imagines these hormones to 

 be collected in the germ-cells and transmitted to the next generation, 

 where their presence contributes to the further development of the 

 special region (when it develops) that corresponds to the region in 

 its parent in which the hormone was made. His speculation meets 

 in the first place with the general objections inherent in Lamarck's 

 theory — objections so well recognized to-day that I need not go over 

 them here. His special appeal to the hormone theory makes use of that 

 theory in a way to which it was never intended to be put, by assuming 

 that an internal secretion formed in one organ can be stored up in 

 another organ, eggs and sperm — an assumption not only unsupported 

 by any evidence, but, as I have stated, one quite foreign to the hor- 



1 The Naturalist in La Plata, W. H. Hudson, London, 1892, pp. 269-270. 



