HARDWICKE'S SCIENCE-GOSSIP. 



151 



and the muscular fibres of the alimentary canal belong 

 to the striped variety. The connective tissue layer 

 forms a thin, structureless basement membrane, firmly 

 united in the cesophagus and crop to the muscular 

 layer and the epithelium. The epithelium consists of 

 scattered nucleated cells, rounded or oval. Where 

 they are deficient the chitinous lining comes in contact, 

 or nearly so, with the basement membrane. These 

 epithelial cells, homologues of the chitinogenous cells 

 of the integument, secrete the transparent and 

 structureless chitinous lining. Hairs (setie) of 

 elongate, conical form, and often articulated at the 

 base, like the large setm of the outer skin, are abun- 

 dant. In the cesophagus they are very long and 

 grouped in bundles along sinuous transverse lines. 

 In the crop, the hairs become shorter and the sinuous 

 lines run into a polygonal network. 



The gizzard has externally the form of a blunt 

 cone, attached by its base to the hinder end of the 

 crop, and produced at the other end into a narrow 

 tube (J to \ in. long), which projects into the chylific 

 stomach. Its muscular wall is thick, and consists of 

 many layers of annular fibres, while the internal 

 cavity is nearly closed by radiating folds of the 

 chitinous lining. Six of the principal folds, the so- 

 called "teeth," are much stronger than the rest, and 

 project so far inwards that they nearly meet. They 

 vary in form, but are generally triangular in cross- 

 section and irregularly quadrilateral in side-view. 

 Between each pair are three much less prominent 

 folds, and between these agam are slight risings of the 

 chitinous lining. A ridge runs along each side of the 

 base of each principal tooth, and the minor folds as 

 well as part of the principal teeth are covered with 

 fine hairs. The central one of each set of three 

 secondary folds is produced behind into a spoon- 

 shaped process, which extends considerably beyond the 

 rest, and gradually subsides till it hardly projects from 

 the internal surface of the gizzard. Behind each large 

 tooth (i.e. towards the chylific stomach) is a rounded 

 cushion set closely with hairs, and again beyond this 

 a second and smaller cushion. There are therefore 

 twelve cushions, in two rows. Still further back the 

 cushions are succeeded by six longitudinal folds, 

 between which are smaller intermediate folds. The 

 whole forms an elaborate machine for crushing and 

 straining the food, and recalls the gastric mill and 

 pyloric strainer of the crayfish. The powerful 

 annular muscles approximate the teeth and folds, 

 closing the passage, while small longitudinal muscles, 

 which can be traced from the chitinous teeth to the 

 cushions, possibly retract these last, and open a 

 passage for the food. The long, tapering extremity of 

 the gizzard is enclosed within the anterior extremity 

 of the chylific stomach, and forms a kind of circular 

 valve. 



The chylific stomach is a simple cylindrical tube, 

 provided at its anterior end with eight (sometimes 

 fewer) ccecal tubes, and opening behind into the 



intestine. Its muscular coat consists of a loose layer 

 of longitudinal fibres, enclosing annular fibres. 

 Internal to these is a basement membrane, which 

 supports an epithelium consisting of elongate cells 

 clustered into regular eminences, and separated by 

 deep cavities. Large simple glands open into the 

 bottom of the cavities. The epithelium forms no 

 chitinous lining in the chylific stomach or coecal 

 tubes, and this peculiarity no doubt promotes absorp- 

 tion of soluble food in this part of the alimentary 

 canal. Short processes resembling thick, stiff cilia, 

 are given off from the free ends of the epithelial 

 cells. 



At the hinder end of the chylific stomach is a very 

 short tube about half the diameter of the stomach, 

 and known as the small intestine. To it are attached 

 60 or 70 long and fine tubules, the malpighian 

 tubules. The small intestine has the same general 

 structure as the oesophagus and crop ; its chitinous 

 lining is hairy, and thrown into longitudinal folds. 

 There are usually six primary folds, which have a 

 radiate arrangement and nearly meet in the centre ; 

 they are often subdivided into minor folds. At the 

 junction of the small intestine with the colon is a 

 circular valve, which nearly closes the passage. A 

 few long setae project from the free edge of the 

 valve. 



From the circular valve the colon extends for 

 nearly an inch. Its diameter is somewhat greater 

 than that of the chylific stomach, and uniform 

 throughout, except for a lateral diverticulum or 

 C£Ecum, which is occasionally but not constantly 

 present towards its rectal end. The fore-part of the 

 colon is thrown into a loose spiral coil. A constric- 

 tion divides the colon from the next division of the 

 alimentary canal, the rectum. 



The rectum is about \ inch long, and is dilated 

 in the middle when distended. Six conspicuous 

 longitudinal folds project into the lumen of the 

 tube. These folds are characterised by an unusual 

 development of the epithelium, the cells lengthening 

 towards the centre of each, while they are altogether 

 wanting in the intermediate spaces, where the 

 chitinous lining blends with the basement membrane, 

 and both are thrown into sharp longitudinal corruga- 

 tions. Between the six epithelial bands and the 

 muscular layer are as many triangular spaces, in 

 which ramify tracheal tubes and fine nerves for the 

 supply of the epithelium. The chitinous layer is 

 finely setose. The muscular layer consists of annidar 

 fibres, strengthened externally by longitudinal fibres 

 along the interspaces between the six primary folds. 



The corrugated and non-epitheliated interspaces 

 may be supposed to favour distention of the rectal 

 chamber, while the great size of the cells of the 

 bands of epithelium is perhaps due to their limited 

 extent. Leydig (Lehrbuch der Histologic) attri- 

 buted to these rectal bands a respiratory function, and 

 compared them to the epithelial folds of the rectum of 



