70 INFLUENCE OF HORMONES 



and a modification of the foot in a water-beetle. 

 Certain organs on the head and pelvic fins of the 

 Chimaeroid fishes are believed to be used for this 

 purpose. 



3. Weapons. — Organs which are employed in 

 combats between males for the exclusive possession 

 of the females. For example, antlers of stags, horns 

 of other Ruminants, tusks of elephants, spurs of 

 cocks and Phasiamidae generally, horns and out- 

 growths in males of Reptiles and many Beetles, 

 probably used for this purpose. 



4. Allurements. — Organs or characters used to 

 attract or excite the female. These might be called 

 the organs of courtship, such as the peacock's tail, 

 the plumes of the birds-of -paradise, and the brilliant 

 plumage of humming birds and many others. The 

 song of birds is another example, and sound is pro- 

 duced in many Fishes for a similar purpose. 



5. Organs for the Benefit of the Offspring : 

 for example, the extraordinary pouches in which 

 the eggs are developed in certain Frogs. In the 

 South American species, Rhinoderma darwinii, the 

 enlarged vocal sacs are used for this purpose. 

 Pouches with the same function are developed 

 in many animals, for instance in Pipe-fishes and 

 Marsupials. Abdominal appendages are enlarged 

 in female Crustacea for the attachment of the eggs, 

 the abdomen also being larger and broader. 



The argument in favour of the Lamarckian 

 explanation of the evolution of these adaptive 

 characters is the same as in the case of adaptations 

 common to both sexes, namely that in every case 

 the function of the organs and characters involves 

 special irritations or stimulations by external 



