14 BRAIN AND BODY OF FISH 



and hatched in the other, the fish from the transplanted eggs, after 

 tlieir journey to the sea, returned to the river in which they were 

 brought up and not to the river in which they were spawned. 

 But they retained their hereditary habit of migrating in the spring 

 instead of in the autumn as do the native fish (E. S. Russell), 



Young salmon in fresh water get to know their home waters and 

 recognise them on their return. They remember the way back to 

 their home river after their extensive journeyings in the sea. 



We see, therefore, that the behaviour of fish is not simply deter- 

 mined by seasons, currents, temperature, and their respiratory 

 needs, as some biologists maintain. Their migrations are as difficult 

 to explain as those of birds. Moreover, like birds, there are many 

 fish which build most efficient nests. The sea stickleback not only 

 builds a nest but binds it together with a thread spun from its own 

 body. The male Lumpfish or Cockpaddle fans the eggs and drives- 

 away all intruders. In the Nile one of the Mormyridse known as 

 Gymnarchus, makes a floating nest of grasses, and the whole nest is 

 somewhat like the ark of bullrushes which served as a cradle for 

 the infant Moses (Cunningham). 



So it appears that nest building, parental care, and the homing 

 instinct are common to fish and birds. A further attribute common 

 to both is song ; it is true that our knowledge of sounds produced 

 by fish is slight, but the hearing capacity of some fish has been 

 stucUed by modem methods and reveals a remarkable range of 

 hearing. The Squeatague produces a deep drumming sound, but 

 only the male, so it is probably used in courting. The Maigre, a 

 Mediterranean fish, is well known for its powers of " song," which 

 it is believed to have given rise to the legend of the Sirens which 

 beguiled Ulysses. Sounds are also produced by the Sea-robin 

 Prionotus. 



I have chosen the title of this book, " The Brain and Body of 

 Fish," because this condenses in a phrase the remarkable fact that 

 the external conformation of the brain of a bony fish indicates its 

 habits and mode of feeding. In other words, the study of the external 

 condition of the brain in bony fish is an index of the development 

 of those organs belonging to the various sensory faculties. The life 

 of a fish consists of two main activities which may be conveniently 

 described under the headings feeding and breechng. The first is 

 necessary for the life of the individual, and the second for the future 

 of its race. In other words nutrition and reproduction make up 

 the life history of a fish. We shall find that not only is hunting 

 a highly specialised function in fisli, but that the various methods of 

 hunting are associated with a varying pattern of brain. For instance. 



