GREA T BRIT A IN. 1 3 



quickly developed, especially in summer, and when placed 

 in a warm and damp place ; this is well seen in members 

 of the cod family. 



There are certain marine fishes, as Argyropelecus, Man- 

 rolicus, &c., which possess luminous organs of a circular 

 form, some resembling impressions and other slight pro- 

 minences of the skin. A form not uncommon on the east 

 coast of Scotland is the " pearl-sides " of Yarrell, Maurolicus 

 Pennantii, having those brilliant spots along the entire 

 length of the abdomen, and even seen on the head. A few 

 years since it was advanced that among these fishes were 

 two kinds of metameric organs, the lenticular and the 

 glandular. Professor Reinhardt was so fortunate as to 

 obtain in the mid-Atlantic two examples of fishes thus 

 provided, and although they merely lived a few minutes 

 after removal from the net, he ascertained with certainty 

 that a light radiated from a spot in the head, flashing, as it 

 were, from thence along the back as far as the first dorsal fin. 



As our knowledge of the forms of animal life which exist 

 at great depths in the ocean has been much increased of 

 late years, a theory has sprang up that the only light 

 existing at these abyssal depths must be derived from the 

 evolution of light from animals, for at these depths fishes 

 are found which are furnished with very large eyes, as if to 

 collect every ray of light which might be present in their 

 vicinity. 



If the exterior of fishes excites our wonder and stimu- 

 lates investigation, no less a field is there in which to 

 extend our inquiries than their internal structure, which, 

 however, I must very briefly, and in a cursory manner, enter 

 upon. 



If we examine the intestinal tract of fishes, we must 

 commence at the anterior end of this canal or mouth, the 



