10 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



formed in watch-glasses. Serial sections of the head, from 3J /x to 10 /a 

 thick, were cut with a Minot-Zimmermann microtome, not only in the 

 three principal planes, but also obliquely. All sections were affixed to the 

 slide with Mayer's albumen mixture, stained on the slide and preserved 

 in xylol balsam. The most satisfactory of many staining methods tried 

 was Kleinenberg's haematoxylin followed by safranin. Victoria green, 

 like safranin, is a good stain for chitin. For differentiating nervous 

 structures, good results followed the use of Vom Rath's picric-osmic- 

 acetic mixture. For elucidating the structure of the glossa and para- 

 glossse, the usetul device of reconstruction in wax from sections was used. 



Mouth, Pharynx, and (Esophagus. 



The external appearance of the mouth has already been described by 

 previous authors, beginning with Nicolet; indeed, the figures of Tullberg 

 and von Stummer-Traunfels are so accurate that my own figure (Plate 1, 

 Fig. 1) is unnecessary, except for completeness. The mouth in repose 

 is tightly closed by the labrum, labium, and palpi, the palpi fitting 

 snugly into apertures on either side of the labrum. When the insect is 

 eating, the tips of the mandibles and maxillae may be seen projecting 

 a little from the mouth to grasp the food, but at other times they are 

 concealed within the capacious pharynx. In no other order of insects 

 is this curious protrusion and retraction of the jaws found. 



The pharynx is evaginated to form four deep pockets, two on either 

 side. In the dorsal and ventral pair of pockets are situated respect- 

 ively the mandibles and maxillae (Fig. 2). The glossa and paraglossse 

 are median in relation to the other mouth-parts (Fig. 3). The lower 

 wall, or floor, of the pharynx is the dorsal surface of the labium, and its 

 upper or anterior wall is formed by the labrum. 



The oesophagus ascends abruptly from the antero-dorsal part of the 

 pharjmx (Figs. 2 and 3), but quickly bends directly backward to the 

 middle of the mesothorax, where it terminates in a valve. The oesoph- 

 agus is a slender tube of uniform calibre, except that the lumen of its 

 anterior portion gradually enlarges from behind forwards. 



The anatomy of the fore-gut has already been studied, especially by 

 Sommer ('85), whose excellent account of Tomocerus applies also to 

 Orchesella in most respects. There is a distinct intima of luiiform 

 thickness (Fig. 4, 2.), which I have shown by chemical tests to be chi- 

 tinous, and in some individuals this is furnished with numerous small 

 and irregular teeth, as mentioned by Sommer. In other specimens, how- 



