102 Instinct and Intelligence 



among the latter are perch, sticklebacks, salmon, 

 and the mudfish. 



The brain of a sea lamprey consists of a 

 slight enlargement of the anterior end of the 

 spinal cord accompanied by a corresponding 

 increase in size of its central canal, and its 

 partial transverse division into three spaces or 

 ventricles. Upon this foundation certain 

 excrescences have been developed in connec- 

 tion with the animal's sensory organs of vision 

 and smell. 1 



The walls of the hind-brain are slightly 

 thickened by the aggregation of nerve cells to 

 form the nuclei, or place of origin of the nerves 

 which supply the animal's respiratory, alimen- 

 tary, and circulatory organs. The hind-brain 

 passes forwards by means of bundles of nerve 

 fibres which extend into the walls of the mid- 

 brain; above these fibres is a part of the brain 

 known as its cerebellum, which in cartilaginous 

 fishes is of small dimensions. The dorsal walls 

 of the lamprey's mid-brain are marked by a 

 longitudinal furrow which separates them into 



1 Catalogue of Museum of Royal College of Surgeons of 

 England, Vol. II., p. 65. 



