THE COD FAINIILY 109 



of this adaptation ; but tlie above observations of the forklieards 

 does not support this theory. The above type of brain, togetlier 

 with the known habits of feeding of B. blennioides, points to the 

 importance of smell and tactile sensation in their hunting equij)- 

 ment. 8ight seems to be of secondary importance and the small 

 facial lobe does not point to a gustatory function of their tentacles. 

 The diversity of form of the swim-bladders of the two forkbeards, 

 we have studied, is remarkable. 



We have already mentioned the tripartite bladder of P. phycis. 

 The swim-bladder of P. blennioides is a thick-walled sac, the speci- 

 men that I have before me is 13 cm. in length, but the anterior 

 lateral prolongations end in a tendon which adds another 1.5 cm. 

 to the length. There are two slight constructions, suggesting a 

 resemblance to the bladder of P. phycis, which divide it into an 

 anterior portion 3 cm. in length, a middle division 4 cm. in length, 

 and a posterior 6 cm. long. The diameters of the three divisions are 

 4 cm., 3 1 cm. and 2| cm. from behind forwards ; there are retia 

 mirabilia in the anterior and middle sections, but the unique feature 

 is the row of appendages on either side about the size of a small pea, 

 about 25 in all on each side. These communicate with the interior, 

 and there are grooves crossing transversely from one to the other. 

 The function of this adaptation of the bladder is unknown, but must 

 obviously not be a sound-producing organ like that of its near 

 relative, P. phycis. 



The study of the lings and the forkbeards suggests an explanation 

 of the function of the acustico-lateral areas. The deep-sea ling 

 differs from M. vulgaris in the size of the acoustic tubercles. The 

 deep-sea blemiy shows no enlargement of these lobes. The deep- 

 sea ling and vulgaris have large somatic-sensory lobes, but these in 

 the P. blennioides are not large. We may argue from this that large 

 acoustic tubercles are of some functional importance to a pelagic 

 predacious fish hunting in the depths in darkness, but are of no 

 value to the sedentary fish hunting by touch. 



The rocklings are a very interesting group of gadoids and com- 

 prise three species, in which there is no separate first dorsal fin, but 

 the front part of the single dorsal is a narrow fringe kept vibrating 

 during life. There are three well-known species. The three- 

 bearded rockling, the four-bearded rockling and the five-bearded 

 rockling. Recently, a fourth species has been identified at the 

 Plymouth Laboratory. As their name implies, the species are 

 distinguished by the number of their barbels, three, four or five, 

 situated on the cliin and upper lip. In the five -bearded rockling 

 there is one barbel on the chin, two on the upper lip, and two on 



