L92 SEXUAL DIMORPHISM 



the spawning process elsewhere, apparently regardless of the 

 exact position of the others. Fertilisation, therefore, in this 

 case, seems to occur quite independently of any special posi- 

 tion or action of male and female in relation to one another, 

 and to be due to mere proximity or congregation. The 

 actual spawning took place, not at night, but between 12 noon 

 and 4 p.m. In this respect the sole differs from the plaice, 

 the spawn of which is shed, in the Dunbar hatchery, according 

 to Mr. Harald Dannevig, the manager of the establishment, 

 usually between dusk and midnight. 



There are other species in which the scales have degen- 

 erated, and in which no differences in their condition occur 

 in the two sexes. This is the case in the Turbot, and also in 

 the Flounder. In the Turbot one scale here and there has 

 become enlarged into a bony tubercle, with a projecting point, 

 while all the rest of the scales have vanished. In the 

 Flounder, at least in the more southern part of its habitat, 

 the scales over the greater part of the body are much reduced, 

 while along the bases of the marginal fins and along the 

 lateral line they have been enlarged into thorny tubercles, 

 each provided with several points. 



In the genus Arnoglossus the males are distinguished from 

 the females by several differences, of which the most definite 

 and conspicuous is the elongation of certain of the fin-rays. 

 This is true at least for the species A. laterna, which has 

 been minutely studied by several naturalists in recent years. 

 As in many other cases, the two sexes were at first described 

 under different names as two distinct species. Specimens in 

 which the secondary sexual characters are not developed had 

 long been described among British fishes under the name A. 

 laterna. The characters of this form are seen in Fig. 20 A, 

 drawn from a specimen 4 inches in length. The fish in this 

 form is frequently taken in the trawl on our south-west coasts, 

 and is a small left-sided flat-fish of no value in the market, 



