220 SEXUAL DIMORPHISM 



fin, while a similar but less marked blue band is situated 

 above the lateral line. The fins are yellow or orange and 

 blue. The female is reddish on the back, but the colour is 

 not so brilliant, and the blue bands are wanting. There are 

 three deep black blotches on the back in the posterior half 

 of the body. The young males are coloured in the same way 

 as the females. Mr. W. Saville Kent observed the courtship 

 of the male of this species in the aquarium of the Crystal 

 Palace, and his description of it, contained in a letter to 

 Nature, is quoted by Darwin. 1 The male had formed "a 

 deep hollow in the sand of its tank, and was endeavouring in 

 the most persuasive manner to induce a female of the same 

 species to share it with him, swimming backwards and for- 

 wards between her and the completed nest, and plainly 

 exhibiting the greatest anxiety for her to follow. The normal 

 brilliancy of this fish was supplemented by a light opaque 

 patch that extended over a considerable portion of the back 

 and shoulders, while the tints of the remaining portion of the 

 body were more than ordinarily deepened." The eggs of some 

 species in this family are adhesive, for instance, Ldbrus 

 maculatus, the commonest British species, while those of 

 others are free. According to Eaffaele 2 the eggs of those 

 species of Ldbrus and Crenilabrus, which are not adhesive, are 

 heavier than the sea-water, while those of other genera are 

 buoyant. Probably, then, the eggs of Ldbrus mixtus are heavy 

 and free, and possibly the male keeps guard over them in the 

 hollow which he makes. Saville Kent's observations prove 

 that the male fish develops nervous sexual excitement in his 

 invitations to the female, and this is associated with a 

 peculiarity of coloration, as in the Dragonet. The elements 

 of the coloration are similar to those of the latter fish, an 



1 Descent of Man, etc., p. 341. 



2 "Uova galleggianti e le larve dei Teleostei nel Golfo di Napoli," Mitt. 

 Zool. Staz., Neapel, Bd. 8, 1888. 



