I'DIS] Alimentary Canal of AJtica Larva 311 



is developed abruptly, as soon as the invagination takes place; 

 it is of course continuous with the perfectly unmodified hypo- 

 dermis just outside. 



In cross and longitudinal sections alike, it is clearh^ to be 

 seen that the glands are composed of a single layer of cells 

 around a common central duct. This chitinous duct is always 

 clear in all of the sections which the writer has examined. The 

 cells are large, and of the cuboidal epithelium type. The nuclei 

 are proportionately large, round or oval, and densely chromatic; 

 the chromatin is in the form of fine granules, except for four or 

 five coarser granules in each nucleus. The position of the 

 nuclei is variable, but usually they are median, or nearer the 

 duct. The cytoplasm is reticular, and seems to consist of a 

 fine net-work. Large vacuoles may appear in the cells, de]Dend- 

 ing on the state of secretory activity. 



There is a delicate limiting membrane outside, which is con- 

 tinuous with the basement membrane of the hypodermis. 



The labial glands, which constitute the prominent salivary 

 glands, or cephalic silk glands, of the Lepidoptera and Tri- 

 choptera, for example, are entirely absent in the larva of the 

 alder fiea-beetle, as in insects of this order generally, both 

 larvae and adults. 



LITERATURE CITED. 



Balbiani; E. G. 18!K). Etudes anatomiques ct histologiques sur la tube digL'stif 



dc'S Cryptops. Arcli. de zoo. exper. ct gen. .ser. 2, t. 8:1-82. ])1. 1-6. 

 Deegener, Johannes Paul Benjamin. 1904. Die Entwicklung des Darmcanals der 



Insectcn wahrend der Metamorphose. I. Cybister roeseli. Zool. lahrb. 



Anat. Bd. 20:-l!)9-fi7(;, pi. 33-43. 

 Leger, Louis and Hagenmuller, Paul. 18!)!). Sur la structure des tubes des Mal- 



pighi de cjuelciues Coleopteres tcncl^rionidcs. Bui. vSoc. Ent. France, 



1899, p. 1!)2-194, fig. 1-2. 

 Plateau, Felix. 1874. Recherches sur les phenomenes de la digestion chez les 



insectes. Mem. Acad. Roy. des Sci. de Belgiciuc. t. 41:1-224, pi. 1-3. 

 Poyarkoff, Eraste. 1909. L'intestin moyen de la galeruque de I'orme pendant 



la metamorphose. C. R. Soc. Biol. Paris, t. 66 (Ixi, i):671-672. 

 1910. Recherches histologic^ues sur la metamorphose d'un Coleoptere (la 



galeruque de I'orme). Arch, d'anat. micr. t. 12:334-474, figs. 1-69. 

 Schindler, Emil. 1878. Beitrage zur Kenntnis der Malpighis'chc^n Gefasse der 



Insectcn. Zeit. f. w. Zool. Bd. 30:587-660. i)l. 38-40 

 Woods, William Colcord. 1916. The Malpighian Vessels of Haltica bimarginata 



vSay (Coleoptera). Ann. Ent. Soc. Amer. v. 9:391-406, pi. 17. 

 1917. The Biology of the Alder Flea-Beetle. Me. Agr. Exp. Sta. Bui. 26."!. 



Since so many good bibliographies of the papers dealing with the alimentary 

 canals of insects are available the writer has included here only those papers to 

 which actual reference has been made in the preceding discussion. 



