252 THE CANADIAN ENTOMOLOGIST. 



or palpiger, though the anterior margin of the mentum is clearly defined. 



There are no true tubercles upon the thoracic or abdominal seg- 

 ments, the setfe thickly studding both dorsal folds of each segment laterad 

 nearly to the spiracle, caudad of which is an area covered with setpe. On 

 the ventral aspect are five areas of setae, the central one being composed 

 of two areas coalesced upon the mesal line. 



Many European writers have described the larvaj of Donacia as 

 having but eight segments, but as Schmidt-Schwedt has pointed out, the 

 ninth and rudimentary tenth are easily recognizable and are very clearly 

 seen in the last embryonic stage, as shown in the figures of Kolliker. 

 Indeed, the latter figures show two long, filiform, lateral appendages 

 attached to each of the ninth and tenth segments. In Lema, Crioceris, 

 and one or two other genera, the anus is found opening in the ninth 

 abdominal tergite, but in Donacia it opens at the caudal margin of the 

 seventh tergite, and true tergites of the eighth and ninth segments are 

 wanting, this space being but slightly chitinized and containing no true 

 sclerites. 



But the most striking feature of the Donacia larvae is the pair of 

 brown, chitinous, sickle-like appendages borne upon the eighth 

 abdominal segment. These are about .5 to .66 mm. in length and reach 

 nearly to the tip of the abdomen. For many years the function of these 

 organs was somewhat of a puzzle to those European entomologists who 

 had studied these larvse, though in 1842 Kolliker gave a clue to their 

 function in his paper on the embryology of D. crassipes, Fab., stating 

 that on the third caudal segment are two cylindrical tubes connecting 

 with the main tracheal trunks (" — atque ex terlio dorso tubuli duo 

 cylindrici cum trachearum truncis communicantes enati sunt ' — Kolliker, 

 Observationesde Prima Insectorum Genesi, etc., Turici, 1842). Ferris, in 

 his excellent article on the larva and life-history of D. sagittaric?., Fab. 

 (Ann. Soc. Ent. Fr. 2d ser. t. VI., 1848, p. 33, PI. II., No. 2, fig. 1-2), 

 stated that their function is wholly unknown. Heeger thought they 

 enabled the larvte to cling to the roots of the plants, and aided them in 

 creeping. 



The manner in which these larvje are enabled to breathe under 

 water and to form a cocoon filled with air has also been somewhat of a 

 problem. At the base of each appendage is what to all appearances is a 

 very large spiracle. Perris thought that these are closed by a thin 

 membrane, but that the air of the tracheal system is purified through 



