78 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



linear series, but the cerebrum still maintains its pre- 

 eminence as the largest of the series. 



Fig. 44. — Reptile brain : A, side view ; B, top view 



Finally, in fishes (Fig. 45) this pre-eminence of the 

 cerebrum is lost and the optic lobes are the largest. In 

 the very lowest fishes, such as the lampreys (Petromy- 

 zon), there is scarcely any enlargement at the anterior 

 end, and in the lancelet [Amphioxus, Fig. 46) the cord 

 is continued into the head with no perceptible enlarge- 

 ment at all. 



Fig. 45. — Fish brain : A, side view ; B, top view. 



In all these gradual changes by which the brain is re- 

 duced finally to a linear series of swellings, it is remark- 

 able to see how persistent are two little organs, the 

 functions of which are still doubtful, one below and one 



Vf he 



Fig. 46. — Amphioxus : spc, spinal cord. 



above the thalamus, viz., the pituitary gland and the 

 pineal gland. These are seen in Figs. 48-53. The use 



