THE COD FAMILY. 285 



to be tactile organs of the same physiological import as that 

 of the cod and the haddock. 



Onos mustela has five barbels and is usually known 

 as the five-bearded rockling, Onos cimhria has four and Onos 

 tricirrata has three ; all have a single barbel on the lower jaw 

 in a position corresponding to that of the cod, and the others 

 are situated upon the snout. 



The young rocklings appear in the nets from March onward, 

 fresh series taking the place of the older forms which by 

 and by, especially in the later months of the year, take to the 

 bottom. It thus happens that up to the end of December 

 specimens of 9 to 9'5 mm. occur. The smaller examples 

 abound in April, May, June and July, an increase in size taking 

 place in certain forms in each series in August, September 

 and October. 



At 3"9 mm. the abdomen posteriorly is covered with black 

 chromatophores externally, and they extend downwards nearly 

 to the vent. They also occur between and behind the great 

 ventral tins, the aspect in this respect approaching that of the 

 four-horned Cottus. Very delicate embryonic rays are present 

 in the marginal fin, chiefly at the base ; the caudal, however, 

 having stronger rays of the same kind. A touch of black 

 occurs on the dorsum over the posterior region of the abdomen, 

 and another on the ventral edge in front of the tail. The 

 ventral fins appear to have reached their maximum length in 

 proportion to that of the fish, being little short of half the 

 total length and of a deep black hue. Four of the rays are 

 especially long, while the fleshy base of the fin is pale, and is a 

 very little in front of the pectoral. At this stage the lower jaw 

 still juts out considerably beyond the upper, especially when 

 depressed. 



At 4 mm. the body is short and thick, with the marginal 

 fin continuous and with very fine embrj'onic rays. Stronger 

 embryonic rays occur in the tail, radiating from the median 

 notochord. A row of black pigment-specks runs along the 

 ventral edge from the vent to the tail. Well-marked black chro- 

 matophores are present on the head and on the dorsum above 

 the bases of the pectorals, and a few specks on the mandible 



