216 SEXUAL DIMORPHISM 



Aphia, is very transparent ; Alalia has scales, but Crystallo- 

 cjdbius is scaleless. The males are much less numerous than 

 the females, and also considerably larger, although they them- 

 selves do not exceed 2 inches in length. The species has 

 lately been proved to be fairly abundant at depths of 30 

 fathoms around the British and Irish coasts. 



The behaviour of these fish during life has not yet been 

 observed, but we may infer by analogy that the males fight 

 together for the company of the females, using their teeth 

 as weapons. This would account for the special development 

 of the teeth, while the greater activity and use of the fins 

 would explain the larger size of the body and greater 

 development of the fins in the male sex. 



The sexual differences in the Lumpsucker are well and 

 widely known, the fish being large and very common on our 

 more northern coasts. The male is much smaller than the 

 female, and more brightly coloured. The colour of the female 

 is a dull blue, while the male is blue on the back and red on 

 the sides and ventral surface. The spawn of this fish is 

 adhesive and the eggs rather large. Large masses of the 

 spawn are frequently seen attached to weed, rocks, or piles 

 between tide marks at low- water springs, and the male is said 

 to be usually found guarding such a mass. The males are much 

 more numerous than the females. Common as the fish are, 

 their behaviour in courtship and in the fertilisation of the eggs 

 does not seem to have been studied, nor has any minute 

 investigation been made of the elements of the coloration in 

 the two sexes. Saville Kent states that he observed the 

 brilliant colours of the male to disappear " after his paternal 

 duties had been discharged." It is highly probable, therefore, 

 that the change of colour is due to the same cause as that 

 which occurs in Callionymus, namely, nervous excitement 

 affecting the secretion of pigment. It is noteworthy that the 

 male of Callionymus is larger than the female, while in 



