6 BULLETIN OF THE BUREAU OF FISHERIES. 
acid. Pilliet (1894) also mentioned some differences between the gastric cells of 
Pleuronectes according as they are situated at the superficial or the deeper portions 
of the gland. 
Pilliet studied principally selachians and Pleuronectes. According to him, the 
glands of the stomach of the selachians are long. In Pleuronectes he noted a differ- 
ence in the extent of the distribution of the glands, in that they are fewer in young 
or undeveloped fish. He likewise claimed that the cardiac portion of the stomach of 
Pleuronectes is essentially peptic, while the pyloric portion is essentially mucous. 
According to Cattaneo (1866), who studied numerous fishes, the fishes highest in 
the scale of evolution repeat in their development the structure of the digestive tract 
as found successively in adult acraniates, cyclostomes, selachians, and ganoids. The 
least differentiated part of the intestine of the higher forms has a structure like the 
most differentiated part of the lower forms. Like Edinger, Cattaneo found in all 
species of fishes that the stomach and middle intestine are the most differentiated 
parts, while the esophagus and terminal intestine preserve a primitive character. 
With Edinger, he concluded that only one kind of cell is present in the gastric 
glands of fishes. 
In addition to the writers already mentioned, Macallum (1886) described the 
intestines of some ganoids, Decker (1887) studied fresh-water fish, while W. N. Parker 
(1889), Hopkins (1890, 1895), Mazza (1891), Mazza and Perugia (1894), Claypole 
(1894), and Haus (1897) have added to our detailed knowledge of the digestive tract 
in fishes. More recently Yung (1899) made a detailed study of the digestive tract of 
Scyllium canicula, while Oppel (1896, 1897, 1900, 1904), in his ‘* Lehrbuch der 
vergleichenden microskopischen Anatomie der Wirbelthiere,” has made a compre- 
hensive review of the previous work on the microscopical anatomy of the digestive 
tract. 
PHYSIOLOGY, 
The first experiments on the digestion of fishes were made by Spallanzani 
(1783), who worked on eels, pikes, carps, and barbels. Previously, Réaumur (1752) 
and Stevens (1777) had worked respectively on birds and man. Réaumur, indeed, 
made the first decisive step in the physiology of digestion. He introduced into the 
stomach of a kite small metallic tubes with the ends covered by a grating of threads 
or fine wire. He found that the gastric juice is acid and that it would digest meats 
and bones, but not vegetable grains or flour. Stevens proved the same thing for 
man, and in addition proved that the gastric juice would digest in vitro. Spallanzani 
in like manner passed into the stomach of his fish tubes filled with flesh, and, having 
left them in the stomach forty-two hours, found them covered with mucus, but with 
little or no flesh within them. From this work Spallanzani concluded that digestion is 
carried on best in the fundus of the stomach. He believed, however, that the stom- 
ach is not the only part capable of digesting food, but that the esophagus, in a more 
feeble way, also has digestive power. He likewise believed that digestion is accom- 
plished without trituration, for the thin tubes which he used did not show any trace 
of deformation. 
Spallanzani also showed that digestion goes on in vitro as in the stomach; con- 
sequently, hypotheses regarding vital force, coction, and fermentation have no 
reason to exist. Digestion is, on the contrary, a chemical phenomenon, not a process 
