114 BRAIN AND BODY OF FISH 



examined. These acoustic tubercles, or acustico-lateral lobes, 

 extend backwards and diminish in size so as to form two lateral 

 ridges, which border the rhomboid fossa and merge into the somatic- 

 sensory lobes. These lobes do not produce any globular swellings 

 as in the ordinary gadoid medulla, but they gradually approach 

 the middle line posteriorly, so as to enclose a triangular area within 

 the apex of which appears a minute lobe divided medially by a 

 depression ; this our serial sections prove to be a small facial lobe. 



To return to the acoustic lobes, it is found that their extent is 

 not only great laterally but also in a dorso-ventral direction. It is 

 also found when serial sections are examined, that the large-celled 

 granular layer of the acoustic tubercles is both wide and deep, and 

 that anteriorly it merges directly into the stratum granulosum of the 

 cerebellum. There is no central acoustic area. The facial lobes are 

 small and are completely overlapped by the somatic-sensory lobes, 

 but the nucleus ambiguus, the motor root of the vagal lobe, is large 

 and extends some distance in a caudo-cephalic direction. It is 

 quite clear that this pictiu-e of the brain of the hake is quite 

 atypical. 



According to Gunther Merluccius has some striking features, 

 " The neural spines of all the abdominal vertebrae are extremely 

 strong, dilated, and wedged into one another. The parapophyses 

 of the third to sixth vertebrae are slender whilst those of all the 

 following abdominal vertebrae are very long and broad, convex on 

 the upper and concave on the lower surface ; the two or tliree 

 anterior pairs are as it were inflated. The whole forms a strong 

 roof for the air-bladder and reminds us of a similar structure in 

 Kurtus." 



If any of my readers should be interested in the remarkable 

 structural differences of the backbone and vertebral spines of Mer- 

 luccius compared with the generalised type of the gadoids, they are 

 referred to a recent account with beautiful illustrations in the 

 Journal of the Marine Biological Association, 1937 (vol. XXII, No 1), 

 by E. Ford. 



Considering the great depths at which the hake is found, it would 

 seem reasonable that this bony canopy has been evolved to give 

 support to the swim-bladder which must be subject to great jDres- 

 sures. The hake is a deep-water fish, having been taken at depths 

 of 400 fathoms, that is to say, approximately half a mile ; it is also 

 oceanic, only approaching the coast occasionally. It is more abun- 

 dant on the south coast of England and Ireland than on the other 

 coasts of the British Isles. It is not caught on the east coast of 

 England and the neighbomdng parts of the North Sea. 



