47 



weeds, usually nearer the surface than the bottom, in an attitude 

 of alertness, with the head poised low and abdomen slightly 

 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. Anai- nymphs are easily recognized by 

 their having lateral spines on but fJ/ree 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 considera])le 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 MoIh(sca. This was principally Anuiirola, the lin- 

 gual ribbons and opercula of which were easily recognized. The 

 molluscan element was estimated as 15 per cent, of the food. 

 Filamentous algae, in quantities too large to be accidental, con- 

 stituted 11 per cent. Cnisfacea were also 11 per cent., nearly 

 all a small amphipod species, Allorchestes dentafa. Of the re- 

 mainder, 56 per cent, was recognized as the remains of in- 

 sects, including larvie of ChiroHOUins, of Strafiontijiidce, of TipuJa, 

 of beetles, of Acjyion, and of a small caddice-fly (^Bltyacopliihi), 

 ^Ya?i\\ Hemiptera,dbnd even the moss-bug (Pe/ocor/s), 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 Asellus 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 



