SKXVAL COLORATION. 255 



species found off the coasts of Southern Australia, the males 

 have three long horns projecting from the head ; if the males 

 of this species were proved to tight for the possession of the 

 females, there would lie a wonderful analogy in these horns 

 to the antlers of deer. 



More striking still is the sexual dimorphism of the Echino- 

 derms. This group includes the sea-urchins, sea-cucumbers, 

 starfish, brittle-stars, and sea-lilies, which are characterised 

 by their radial symmetry, and by the presence of a calcareous 

 skeleton, more or less perfect, beneath the true skin ; they 

 are not active animals as a group, though the Conuitiilu can 

 swim as well as crawl, and some of the starfish and brittle- 

 stars can move about with a certain degree of rapidity ; many 

 of them have eyes. Some of these echinoderms are among 

 the most brilliantly coloured of marine invertebrates, but the 

 colours can hardly have much significance, for the reasons 

 stated in considering the fauna of the deep sea. 



Sexual differences have been discovered to exist in a good 

 many species.* These differences may be seen extended to 

 the colour of the sexes, for Oscar Schmidt in " Brehirfs 

 Thierleben," p. 981, remarks that the males of Xt>'og>/lo- 

 centrotux Ucid/ts (a common sea-urchin) are darker coloured, 

 while the violet tint of the females tends more towards red. 

 Prof. ( 1 amerano,f while disinclined to admit any constant 

 differences in colour, abundantly confirms Prof. Schmidt's 

 description of other sexual differences in form and size. 

 There can here be no question of preference in either sex, 

 for the ova and sperm are, as in the case of worms, simply 

 shed into the surrounding water. It should perhaps be re- 

 marked that secondarv sexual characters, other than colour, 



t< j* ~^^^__ 



* Zool. Anzeiger., vol. iii., a paper by Prof. Studer 

 t Boll. Mus. Zool Torino, Nov. 1890. 



