Chap. XIII.] THE COCKROACH. 265 



exoskeleton at the mouth ; (2) the mesenteron, without chitinous 

 lining ; (3) a proctodceal section, lined with a chitinous infolding 

 of the posterior integument. Each section is provided with 

 appendages: (1) the salivary glands and receptacles, stomodseal; 

 (2) the ccecal tubes, mesenteric ; and (3) the Malpighian tubules, 

 proctodseal. 



The mouth leads into a buccal cavity, into which there 

 projects a lingua (li.), or tongue-like process, supported by 

 chitinous plates. Beneath the lingua opens the common duct 

 of the salivary glands and their receptacles. Each salivary 

 gland consists of two principal lobes and a small (anterior) 

 accessory lobe on each side. There is also on each side an 

 elongated salivary receptacle. The ducts of both glands and 

 receptacles are lined with delicately-ribbed chitinous membrane, 

 the finer branches of the salivary ducts end in secreting bulbs 

 or acini. The student must examine a gland and its ducts under 

 the microscope. The two glandular ducts unite in the middle 

 line into a common duct ; the ducts from the receptacles do the 

 same ; then both these unite into the salivary duct which opens 

 beneath the lingua. The salivary secretion is neutral, and trans- 

 forms starch into glucose. 



The gullet is narrow, pierces the nerve-ring, passes through 

 the occipital foramen, traverses the neck, and then, in the 

 thorax, gradually widens into the large crop (cr.), which is at 

 once followed by the muscular gizzard (gi.). The chitinous lining 

 of the gizzard is differentially thickened, so as to form a circlet 

 of six teeth, two of which are shown in 81, B., and one, in side 

 view, at C. Between the main teeth are finely-toothed ridges. 

 The toothed part of the gizzard is followed by six prominent 

 setose cushions. The function of the toothed part of the gizzard 

 is to act as a gastric mill, while the setose cushions act as 

 strainers. Some observers, however, contend that, both in the 

 cockroach and in the crayfish, the so-called gastric mill is to be 

 regarded as part of the straining apparatus, and not as a divider 

 of the food. In any case it would tend to squeeze the food pulp. 

 The gizzard ends in a tubular portion which protrudes into the 

 cavity of the succeeding portion of the canal. 



