CONTRIBUTIONS FROM THE BIOLOGICAL LABORATORY OF THE BUREAU OF FISHERIES AT WOODS HOLE, MASS. 
THE PHYSIOLOGY OF THE DIGESTIVE TRACT OF ELASMOBRANCHS. 
By MICHAEL X. SULLIVAN, Pu. D. 
INTRODUCTION. 
The digestive tract in fishes has been studied quite extensively both from the 
histological and from the physiological standpoint. Most of this work has been done 
on European species, however, and has given rise to contradictory conclusions, 
especially from the viewpoint of physiology. Hence it seemed advisable to devote 
some attention to fishes found also in American waters, and I have accordingly 
undertaken the study of the digestive tract of elasmobranchs.“ 
This group of fishes was chosen for investigation, first, because of the relatively 
simple structure of their digestive tract, and second, because they may, from their 
position in the scale of evolution, form the groundwork for an extensive comparative 
study of fish in general. Thus we may arrive at a unified view of the changes, 
structural and physiological, which have taken place in the alimentary canal of fishes 
from the lowest to the highest. The treatment of the subject is partly histological, 
but mainly physiological. 
HISTORICAL DISCUSSION. 
THE DIGESTIVE TRACT IN FISHES. 
MORPHOLOGY. 
As in higher animals, the digestive tract in fishes may be divided into the 
following portions: Mouth, esophagus, stomach, small and large intestine. In 
fishes, however, two or more of these divisions may coalesce and become indistin- 
guishable. Asa rule there is a complicated dentition, but no salivary glands. The 
buccal cavity opens directly into the esophagus, and this in turn into a large stomach, 
aThe work embodied in this paper was done at the laboratory of the U. S. Bureau of Fisheries, Woods Hole, Mass. 
during the summers of 1905 and 1906, when the writer was a salaried assistant of the Bureau. I am indebted to Dr. W. L. 
Chapman for making the photomicrographs of the rectal gland (plate I). 
