486 LIFE : OUTLINES OF GENERAL BIOLOGY 



of Paradise and humming-birds, the tail of the lyre-bird, the neck- 

 feathers of the ruff, the cock's spur, the great bustard's inflatable 

 throat-pouch. Among reptiles there are a few cases like the erectile 

 dorsal crest of Anolis cristatus and the bony horns of some chamae- 

 leons. Among amphibians there are the dorsal crests of some newts, 

 the swollen first fingers of frogs and toads, the resonating sacs of 

 some frogs. Among Fishes, we recall the old male salmon's hooked 

 lower jaw, the brilliant colouring of the male dragonet, the "claspers" 

 of Selachians. Among Invertebrates, there are well-known contrasts 

 between the sexes in the Argonaut, in the Giant Japanese crab, in 

 many spiders, in Djmastid and Lucanid beetles, and in many 

 Lepidoptcra. Cunningham notices the dimorphism in Nereis, and 

 the case of the female Bonellia with her pigmy mate is famous. 

 In most cases the positive character is on the male side. He has an 



IG. 68. 



Sex Dimorphism in a Small Fish {Phallosletlius diinckeri). After Tate Regan. 

 The smaller male (M) carries a relatively large clasping organ, situated 

 anteriorly. It is, naturally, undeveloped in the larger female (F). 



extra something which the female does not possess in a developed 

 state, if at all. It is important therefore to' recall two or three 

 examples of the converse. The females of the frog genus Nototrema 

 have a pocket on the back into which tlie male pushes the eggs. So 

 far as we know, the marsupium or pouch of Marsupials is never more 

 than a rudiment in the males. In the Kcd-necked Phalarope the 

 female is the more decorative bird. 



After a survey of sex-characters, it is well to remind ourselves that 

 conspicuous difference between the sexes is the exception, and 

 general similarity the rule. In many of the higher animals the males 

 and females arc very like one another in external appearance. 

 Cat, mouse, rabbit, and hare may be mentioned among mammals; 

 rooks, kingfishers, and many parrots among birds. Below the level 

 of crustaceans, in animals like starfishes and sea-urchins, marine 

 worms, threadworms, jellyfish, and corals, it is rare to find more 

 than hints of sex-dimorphism. 



