160 BRAIN AND BODY OF FISH 



phycis blennioides of a sedentary habit, and not a predacious fish, 

 it will be clear that it is not only a deep sea habitat that is responsible 

 for large acoustic tubercles. Molva elongata hunts not only at 

 great depths, but is essentially a predatory fish so that two concUtions 

 must be present to cause the great enlargement of the acoustic 

 tubercles. These considerations are confirmed by what we have 

 noted in the pattern of the hake's brain. The cerebellum is small 

 and on either side are two globular projections in the position 

 of the acoustico-lateraUs areas, from which two ridges pass posteriori}- 

 and then converge and meet at the caudal end of the medulla. 



It must be mentioned that the hake is a near relative of the cods, 

 and strictly is a species of the Merlucciidae. Its habits we have 

 described ; it is a mid-water feeder, but descends to from 300 to 

 400 fathoms in the winter. It is suggested that the hake, like 

 molva elongata, has this great development of the acoustic tubercles 

 in association with its bathysmal and predatory habits. A still 

 more remarkable confirmation of these suggestions is the pattern 

 of brain in four deep-sea fish of marked predatory habits, all members 

 of the Trichiuridae, Athanopus carbo, Lepidopus caudatus, Pro- 

 methichthys and Nesiarchus nasutus. In these fish the acoustic 

 tubercles are enormous and the somatic-sensory lobes also large. 



It is known that in the deep sea at a depth of two hundred 

 fathoms light does not penetrate. According to Cunningham 

 it is certain that fish, that habitually live beyond this depth, show 

 enlargement of the dermal sensory tubes. We have seen that the 

 deep sea fish such as the scabbard fish and the hake have a special 

 enlargement of the acoustico-lateral area so as to produce a definite 

 lobe, and it is a justifiable assumption to associate this condition 

 with the enlargment of the sensory canals. How are the fish in 

 complete darkness able to find their prey ? They may be able to 

 detect its presence by smell, but it is doubtful at what distance 

 this would be possible, and whether smell could give any exact idea 

 of the position of the prey. It has been pointed out that the 

 lateral-line organs, situated at intervals along the side of an elongated 

 body, would receive different impressions from a moving body, 

 that was the source of waves, according to the angle these un- 

 dulations hit the side ; and it is obvious that when the pursuer 

 was heading for the prey the waves would have a very different 

 effect than if the undulations were received obliquely. It is also 

 known that the lateral-line organs perceive vibrations of water, and 

 react to them in the same way that the similar organs of the semi- 

 circular canals do. The conclusion is therefore drawn that the 

 enlarged acoustic tubercles of deep sea fish are organs for direction 



