47 
weeds, usually nearer the surface than the bottom, in an attitude 
of alertness, with the head poised low and abdomen shghtly 
elevated. Its locomotion is relatively rapid, accomplished 
either by walking or by ejecting water from the respiratory 
chamber. It is notoriously cannibalistic. In the midst of 
abundant and choice food the larger nymphs will eat the smaller 
of their own species, and two of equal size may not safely be 
kept in close quarters. Anar nymphs are easily recognized by 
their having lateral spines on but three abdominal segments pre- 
ceding the last. The young nymphs have wide alternating 
transverse bands of brownish and white, but become in later 
life a nearly uniform green or brownish green. 
To get a definite idea of the food of the nymph, the stom- 
achs of a considerable number, taken at different dates and in 
various situations, were examined by Mr. Hart. Thirteen of 
them contained small quantities of comminuted food, the most 
unexpected feature of which was the large quantity of remains 
of univalve Mollusca. This was principally Amnicola, the lin- 
gual ribbons and opercula of which were easily recognized. The 
molluscan element was estimated as 15 per cent. of the food. 
Filamentous alge, in quantities too large to be accidental, con- 
stituted 11 per cent. Crustacea were also 11 per cent., nearly 
all a small amphipod species, A//orchestes dentata. Of the re- 
mainder, 56 per cent. was recognized as the remains of in- 
sects, including larve of Chironomus, of Stratiomytide, of Tipula, 
of beetles, of Ayrion, and of a small caddice-fly (Rhyacophila), 
small Hemiptera, and even the moss-bug (Pe/ocoris), the sharp 
sting of whose beak often temporarily interrupts the routine of 
station field-work. A nymph was observed by us to attack a 
crawfish three fourths of an inch long, and devour its abdomen. 
Young nymphs in a breeding-cage ate Ase//us eagerly. 
In the vegetation-filled waters everywhere about Havana 
these nymphs developed in great numbers, while in the Missis- 
sippi and associated waters about Quincy, in which vegetation 
is comparatively scanty, Mr. Garman found but few individuals. 
Our specimens of the nymph were taken from a remarkable 
