288 THE COD FAMILY. 



There were thus made known to science three species of 

 Gouchia exactly corresponding to the three known rocklings, 

 and although Couch remarked upon the ' analogy ' of the two 

 groups, it was left to Day and others to show that the genus 

 Gouchia included simply a series of young forms belonging to 

 the genus Onos or Motella (rocklings). 



THE FIVE-BEARDED ROCKLING. (Onos mustela, L.) 



The development of the five-bearded rockling is best known. 

 The ripe female is greatly distended and the eggs may be 

 extruded by the slightest pressure ; this is due to the fact that 

 a great number of the eggs ripen at the same time, whereas in 

 a number of allied species there is a gradual ripening and 

 extrusion of the contents of the ovary. Dr Raffaele calls 

 attention to the same peculiarity in the three-bearded species. 



The spawning-period of the five-bearded rockling appears 

 to extend from April to August (inclusive), as during these five 

 months the egg is one of the commonest on the east coast : it 

 is abundant in all parts except the region of Smith Bank, so 

 that not only is the spawning-period one of the most prolonged, 

 but the distribution is perhaps the most general of all the 

 fishes which come under our notice. This extended distribution, 

 in time and place, must be a valuable safeguard to the preser- 

 vation of a species destined to be devoured by others. 



The egg is pelagic, spherical, of small diameter ('028 

 inch, '72 mm.), and is furnished with a yellowish oil-globule 

 ('0033 inch, '024 mm.). In this feature as in several characters 

 of the post-larval stages the rockling gives evidence of its close 

 genetic connection with the ling. The capsule of the egg ' is 

 slightly corrugated and the entire yolk-surface presents a 

 series of minute oleaginous particles.' During the month of 

 May, the period of incubation at St Andrews 1 Laboratory 

 extended over 10 days, whilst the late G. Brook 2 in his own 

 sheltered laboratory at Huddersfield, and at a later season of 



1 Mclntosh and Prince, pp. 677 and 832. 



2 G. Brook, Jonrn. Lin. Soc. p. 273. 



