FORE-GUT OF CORYDALIS CORNUTUS L. 587 



are most heavily chitinized and meet, almost completely closing 

 the lumen. The lumen can readily be closed by the concerted 

 action of the circular muscles and the longitudinal muscles 

 directly attached to the teeth. 



Internally the gizzard presents a remarkable appearance (fig. 4). 

 It is provided with six large, inward-projecting, chitinous ridges 

 and alternating with these are six smaller ridges (fig. 4, l.r., s.r.). 

 Each large ridge consists of two prominent teeth, an anterior 

 {a.t., figs. 5 and 6) and a posterior one (p.t.), separated by a deep 

 constriction. The anterior tooth projects caudad, the proximal 

 part being somewhat narrow and sharp along its inner edge. It 

 rapidly becomes broader, more strongly chitinized and fits closely 

 over the base of the posterior tooth. Its entire surface is clothed 

 with setae which are longer and more numerous along the poste- 

 rior border. 



Though scarcely distinguishable in surface view the posterior 

 teeth are of two types (compare fi.gs. 5 and 6). They alternate 

 with each other, three of each in a gizzard. The one shown in 

 figure 5 appears in side view somewhat like a pistol, the internal, 

 posterior projecting process answering to the hammer. Viewed 

 posteriorly it presents a broad, somewhat hollowed surface, nar- 

 rowed on its anterior margin into a sharp tooth projecting caudad. 

 The other type is shown in figure 6 and differs from the first in 

 the lack of the anterior process. 



The small longitudinal ridges (figs. 4 and 7, s.r.) project 

 between the larger ridges, almost completely filhng the interven- 

 ing spaces. They are not divided into teeth, though at their 

 posterior ends each one presents a broader, setiferous portion 

 projecting caudad. 



The epithelium of the gizzard consists of a layer of flattened 

 cells with fairly well defined cell walls. In the tips and sides 

 of the longitudinal ridges the cells are crowded and narrowly 

 elongate. The nuclei are oval to spherical with densely staining 

 granules. The cytoplasm is granular and more or less strongly 

 vacuolate in the cells lining the ridges. The vacuoles are located 

 at the bases of the cells. The longitudinal ridges are filled with a 

 non-cellular tissue (fig. 9, st) which is usually designated as a 



