14 A. S. PACKARD, JR., ON THE ANATOMY 



The minute structure of the vertical folds of the first or anterior division of the crop 

 may be seen at plate 5, figs. 1, 2, where the relations between the muscular, epithehal 

 and chitinous layers are shown. The limits between the longitudinal striated muscular 

 layer (m) and the epithelial layer are clear and well marked, the Imndles of pavement 

 epithelimn {pe) running at right angles to and abutting directly on the muscular layer. 

 The pavement epithelium is also, in slices stained with haematoxylin, clearly demarked 

 from the columnar epithelium (ce) by its pale lilac tint, the latter staining brownish and 

 contrasting well with the purple-stained chitine, which is finely laminated, the lines of 

 deposition being waved, the points of the waves under a low power appearing like fine 

 lines passing inward near Imt not quite to the free edge of the tooth, the margin of the 

 chitinous layer remaining unstained and pale yellowish. Fig. 2 represents the small 

 central tooth la-, still more enlarged, showing the lines of growth of the chitin, and the 

 rufile of columnar epitheUum, indicated by the row of large nuclei bordering the margin 

 of the lobes of the columnar epithelium layer. 



In the teeth of the middle region, which as we said, number some 225, the columnar 

 epithelium is wanting, though the corresponding tract is yet stained pale brown by haema- 

 toxylin or deep crimson by carmine, but the cells are of the same nature as in the adjoin- 

 ing pavement epithelium ; it is also not scalloped, but the layer of chitine is much thicker 

 than elsewhere in the digestive canal. 



The proventricular cone or tube has internally aljout thirteen unequal chitinous folds, 

 continuous with and like those of the oesophagus, five large folds alternating with eight 

 smaller ones. The folds are yellowish, and project ruffle-like at the end, contrasting in 

 structure and color with the whitish exterior of the cone or strainer. An examination of 

 the cellular structure of the interior lining of this tube, shows that it has a chitinous 

 linino- continuous with that of the crop, and which stops at the ruflfle-lilce extremity of 

 the tube ; this chitinous layer is succeeded within liy a ruftle-like layer of columnar 

 epithelium, like that in the fore part of the crop. The chitin is entirely wanting in the 

 papillose exterior of the tube, while the layer of columnar epithelium is deep, the cells 

 being very long and slender. The structure, then, of this tube is externally lil^e that of 

 the stomach walls as described below, while internally it is histologically an extension of 

 the structure of the oesophagus and proveutriculus. 



The beginning of the mid-gut or true stomach, as we regaixl it, is lined internally with 

 a layer of large, long, erect papillae which extends nearly as fiir as opposite the end of 

 the strainer, and is also extended along the outside of this organ. Just before a point 

 opposite the end of the strainer, this layer of dense close-set papillae suddenly stops, and 

 is succeeded by a division of the digestive canal lying between the point opposite the end 

 of the proventricular strainer, and a point situated a little before the opening of the 

 first pair of biliary ducts. This region, which we regard as the true stomach, has the 

 inner surface raised into about twelve transverse or circular folds. Just where this region 

 of tlie digestive canal ends, it contracts, and this is judged to be the line of demarcation 

 between the mid-gut and hind-gut, i. e., the true stomach and the intestine. It should 

 be observed that the chitinous folds of the oesophagus and proventricle (usually called 

 stomach) are continuous, alike morphologically, and stop at the posterior end of the 

 proventricular strainer. It is evident that the food, such as worms, at first partly torn by 



