PLECOPTERA NYMPHS OF NORTH AMERICA = 5 
In the carnivorous type (Perlidae) the mouth parts are built 
very differently. The labrum is very wide and short and is pro- 
vided with a fleshy epipharynx which may protrude beyond the 
anterior margin of the labrum, or may be retracted underneath. 
The elypeal suture is obsolete. The mandibles are quite slender, 
the teeth are long and sharp, and the molar is lacking. The maxil- 
lae are slender. The lacinia terminates in either one or two long, 
sharp incurved teeth, fitted for holding prey. The galea is much 
reduced in size and apparently is almost without function. The 
maxillary palpus is long and slender. The labium is large; the 
glossae are reduced to small triangularly rounded lobes, while 
the paraglossae are enlarged into big lobes. The labial palpi are 
long and slender. 
In addition to the differences in the structure of the mouth- 
parts, the herbivorous nymphs are generally more cylindrical in 
shape, more or less concolorous, and are found more often in 
small, upland, spring brooks, and in quieter waters where vege- 
table material accumulates. The carnivorous nymphs, on the other 
hand, are usually more flattened, more strikingly colored, and in- 
habit chiefly the larger and swifter waters. 
A eareful study of the musculature of the mouth parts in the 
two types shows many differences, and the structures of the di- 
gestive tract in the herbivores are different from those of the 
earnivores. Examination of stomach contents often reveals plant 
material, such as diatoms, etc., in the carnivorous nymphs, but 
such material is probably ingested incidentally to capturing ani- 
mal prey, although in the early stages the nymphs apparently 
feed partly on algae. Similarly, one may. find at times small ani- 
mals, such as protozoans and crustaceans, in the digestive tracts 
of the herbivores. 
RESPIRATION 
Respiration is of the closed or apneustic type. The nymphs 
either absorb oxygen directly through the integument, or through 
tracheal gills. Many species lack gills altogether ; some forms, like 
Perlodes, Peltoperla and a few others possess only a few single 
gill filaments, while others, such as Pteronarcys, Acroneuria, and 
Perlinella, are provided with many copious gill tufts. Wu (57) 
found what he considered retractile anal blood gills in Nemoura 
vallicularia. In this species he found also that ‘‘part of the res- 
piratory function is performed by tufts of tracheoles that arise 
from the tracheal branches of the body and extend outward to lie 
immediately entad of the thin ventral body wall. These tufts are 
