folsom: mouth-parts of orchesella cincta. U 



ever, no such structures are observed, and, if they are not artificially 

 produced, their presence may possibly depend upon the interval which 

 has elapsed since the last moult, the intima being shed and replaced at 

 every moult. The epithelial wall consists of a single, well developed 

 layer of pigmented cells (Figs. 3 and 4, eHh.). The boundaries of the 

 individual cells are not well indicated, but the arrangement of their 

 large round or oval nuclei is an indication of their size. These cells, 

 being doubtless of ectodermic origin, are, like the permanent " hypoder- 

 mal " cells, pigmented ; the pigmentation extends back through the 

 whole length of the oesophagus to the stomach. The epitlielium 

 is thrown into four or five prominent longitudinal ridges (Fig. 4). 

 A delicate hyaline and homogeneous basement membrane {mb. ba.) 

 is distinguishable, surrounding which is a single layer of circular 

 or constricting muscles (Figs. 3 and 4, c'stt.). Around the anterior 

 portion of the oesophagus, which Sommer designates as pharynx, the 

 muscle fibres are quite stout, but farther backward they gradually 

 decrease in size, as do their nuclei also, and finally disappear near the 

 base of the head. As there is but one nucleus to each circular fibre, 

 the statement of Sommer ('85, p. 696) that " Jeder Eing entspriiche 

 hiernach vielleicht je einer Muskelzelle " is unnecessarily cautious. The 

 nuclei of the circular muscles lie, as others have observed, in a single 

 (median dorsal) line (Fig. 3, nL), and each nucleus is contained in a loose 

 sheath which is external to the muscle proper. The condition in 

 Orchesella is so nearly identical with that of Macrotoma [Tomocerus] 

 that I can apply Sommer's ('85, p. 691) description without change to 

 the former species : " Die Muskeln zeigen eine zarte feinkornige Aus- 

 senschicht, Perimysium, in welcher in ziemlicher Anzahl kleine runde 

 Kerne eingelagert sind. Dieses Perimysium ist besonders machtig an 

 den Muskelbtindeln des Kopfes entwickelt." There are no longitudinal 

 muscles enclosing the constrictors. All the muscles in the head are 

 conspicuously striated, and, in Sommer's ('85, p. 691) words, "Die im 

 Korper sich findenden Muskelbtindel sind von verschiedener Dicke, die 

 einfachsten bestehen wohl aus einer einzigen Muskelfaser, wahrend die 

 starkeren aus einer Anzahl von Primitivbtindeln zusammengesetzt sind, 

 wie man an Querschnitten leicht sehen kann. Die Insertion der Muskel- 

 btindel an die Chitincuticula erfolgt nicht unmittelbar, sondern mittelst 

 einer Sehne." 



The pharynx and oesophagus are dilated by means of thirteen pairs 

 of muscles (Fig. 3, dil.), situated as follows. Four short muscles 

 (Fig. 3, dil. phy.) originate on the clypeus in paramedian positions, and 



