1901.] NATURAL SCIENCES OF PHILADELPHIA. 711 



valvular fold. Here is certainly the division line between ectoder- 

 mal and entodermal derivatives. 



The characteristic absorptive cells of the middle intestine, fig. 

 34, Abs.C, are long slender cells, about .14 mm. high, rather 

 flattened at the base and inserted by slender lateral processes into 

 the basement membrane, B.M., and bearing several very long cilia, 

 CIL, on the distal surface. The cilia are about as long as the cell, 

 and are inserted on a basal knob. The nucleus is rather elon- 

 gate, and is situated near the base of the cell. The cell contents 

 are of a variable nature; usually the cell is filled with a finely 

 granular pink -staining substance, h?ematoxylin-eosiu stain, in 

 which are numerous spherical masses that stain a dark red. Other 

 cells present a vacuolated appearance, as if filled with a foamy 

 fluid substance. Since the function of these cells is absorption, 

 the different appearance of the contents should correspond to the 

 different stages in the absorptive process. Throughout the greater 

 part of the middle intestine the cells are swollen with the food con- 

 tents, and so closely pressed together that it is impossible to make 

 out the details of a single cell. All cell walls have apparently 

 disappeared, and the result is a chaotic mass of cytoplasm filled 

 with globules and granules of food, bordered by cilia on the side 

 toward the intestinal lumen, and with a row of nuclei along the 

 base, above the basement membrane. 



The gland cells that have been mentioned as occurring occa- 

 sionally in the middle intestine, fig. 34, Gl.i, cannot be distin- 

 guished from the absorptive cells — except by their absence of cilia — 

 in preparations stained with iron-hsematoxylin, since with this stain 

 both the secretion globules and the absorptive particles stain black. 

 With the hi3ematoxylin-eosin staia, howev^er, the differences are 

 strongly brought out, the food granules staining a brighter red, 

 and having a different degree of refraction from that of the gland- 

 ular secretion globules. 



It has already been mentioned that the two anterior pouches 

 consist of different histological elements from the subsequent ones. 

 They are also somewhat smaller and are deflected slightly forward 

 (see fig. 1). In the more anterior part of the middle intestine, the 

 ca?ca are but little deeper than the axial part of the canal, but 

 farther back the cseca increase in depth at the expense of the axial 

 portion. 



