438 - Mr. Newrort on the Anatomy and | 
Perla and Sialis in the general character of its respiratory organs, but it dif- 
fers from them in other parts of its structure. 
Alimentary Canal.—The alimentary canal (fig. 10) consists in chief part of 
an enormously elongated cesophagus (m), which, instead of joining with the 
stomach (p) in the metathorax, passes backwards, accompanied by the tra- 
— chez (4, /), as far as the fourth segment of the abdomen, and then terminates 
in the digestive organ, which does not exhibit even the smallest rudiments of 
gastric glands, which exist of large size in Perla (fig. 12 o). This proves as 
marked a difference in the habits of these two genera as exists between these and 
Sialis (fig. 13), in which the cesophagus is extended backwards in the form of 
a pouch (n), as in the Diurnal Lepidoptera. The stomach (p) of Pteronarcys 
differs as much from that of Perla as the esophagus. It is capacious, mus- 
cular, and of considerable length, forming two or three convolutions before it 
terminates in a pylorus, around which the Malpighian vessels are inserted; 
whilst that of Perla abnormis is surrounded at its cardiac origin by six large 
czecal glands (o), is short, somewhat funnel-shaped, straight, and has no con- 
volution. In these respects the stomach of Perla resembles that of the Blat- 
tide. In the number, appearance, size, and place of insertion of the Malpi- 
ghian vessels (r), Pteronarcys resembles Perla, but both differ from Sialis, in 
which there are only six of these vessels, while in the others there are from 
forty to fifty. These three genera also differ as regards the ilium ( q), and the 
form and size of the colon (9.21m Pteronarcys and Sialis the ilium is short 
and slender, but it is more than twice as long in Perla. The colon in the 
latter is very muscular, is almost as large as the stomach itself, and has a 
cæcum projecting from it. In Sialis the colon is larger than the stomach, 
and has a small lobulated cæcum at its commencement, as in Lepidopterous 
larva; but in Pteronarcys it is shorter and much smaller than in either of 
these genera. These differences in organization indicate differences in kind of 
food, or in habit and economy, and establish the distinctness of the genera. 
The existence of gastric glands.in Perla Shows that this genus stands at the 
head of its family, and approaches the Orthoptera ; while the absence of these 
in Pteronar cys, and in the smaller Perlide, Nemoura, shows also that thes 
genera are of a type inferior to Perla. | 
Nervous System.—The nervous system of Pteronarcys (fig. 14) leads us to a 
