COPROLITES. 153 



the small intestine, we have additional evidence to show 

 even the form of the minute vessels and folds of the mucous 

 membrane, by which it was lined. This evidence consists 

 in a series of vascular impressions and corrugations on the 

 surface of the Coprolite, which it could only have received 

 during its passage through the w^indings of this flat tube.* 

 Specimens thus marked are engraved at PI. 15, Figs, 3, 5, 

 7, 10, 12, 13, 14. 



If we attempt to discover a final cause for these curious 

 provisions in the bowels of the extinct reptile inhabitants of 

 the seas of a former world, we shall find it to be the same 

 that explains the existence of a similar structure in the 

 modern voracious tribes of Sharks and Dog-fish.f 



As the peculiar voracity of all these animals required the 

 stomach to be both large and long, there would remain but 

 little space for the smaller viscera ; these are therefore re- 

 duced, as we have seen, nearly to the state of a flattened 

 tube, coiled like a corkscrew around itself; their bulk is 

 thus materially diminished, whilst the amount of absorbing 



* These impressions cannot have been derived from the membrane of the 

 inferior large intestine, because tliey are continued along those surfaces of 

 the inner coils of the Coprolite, which became permanently covered by its 

 outer coils, in the act of passing from the spiral tube into this large intes- 

 tine. 



t Paley, in his chapter on mechanical compensations on the structure of 

 animals, mentions a contrivance similar to that which we attribute to the 

 Ichthyosaurus, as existing in a species of Shark, (the Alopecias, Squalus 

 Vulpes, or Sea Fox.) " In this animal, he says, the intestine is straight 

 from -one end to the other : but, in this straight, and consequently short in- 

 testine, is a winding, cork-screw, spiral passage, through which the food, 

 not without several circumvolutions, and in fact by a long route, is con- 

 ducted to its exit. Here the shortness of the gut is compensated by the 

 obliquity of tiie perforation." 



Dr. Fitton has called my attention to a passage in Lord King's Life of 

 Locke, 4°. p. 166, 167, from which it appears that the importance of a spirsil 

 disposition within the intestinal canal, which he observed in many prepara- 

 tions in the collection of anatomy at Leydcn, was duly appreciated by tiiat 

 profound philosopher. 



