128 THE COCKROACH: 



formed opens into the much larger common receptacular duct, 

 formed by the union of paired outlets from the salivary reser- 

 voirs. The common salivary duct opens beneath the lingua. 

 Each salivary reservoir is an oval sac with transparent walls, 

 and about half as long again as the gland. The ducts and 

 reservoirs have a chitinous lining, and the ducts exhibit a 

 transverse marking like that of a tracheal tube. When 

 examined with high powers the wall of the salivary gland 

 shows a network of protoplasm with large scattered nuclei, 

 resting upon a structureless chitinous membrane. 



The salivary glands are unusually large in most Orthoptera.* 

 In other orders the} r are of variable occurrence and of very 

 unequal development. 



The Ccecal Tubes. 



There are eight (sometimes fewer) coecal tubes arranged in a 

 ring round the fore end of the chylific stomach; they vary in 

 length, the longer ones, which are about equal to the length of 

 the stomach itself, usually alternating with shorter ones, though 

 irregularities of arrangement are common. The tubes are 

 diverticula of the stomach and lined by a similar epithelium. 

 In the living animal they are sometimes filled with a whitish 

 granular fluid. 



Similar csecal tubes, sometimes very numerous and densely 

 clustered, are attached to the stomach in many Crustacea and 

 Arachnida. The researches of Hoppe Seyler, Krukenberg, 

 Plateau, and others have established the digestive properties 

 of the fluid secreted in them, which agrees with the pancreatic 

 juice of Vertebrates. 



The Malpicjhian Tubules. 



The Malpighian tubules mark the beginning of the small 

 intestine, to which they properly belong. They are very 

 numerous (60-70) in the Cockroach, as in Locusts, Earwigs, and 

 Dragon-flies ; and unbranched, as in most Insects. Thev are 



o 



about '8 inch in length, and '002 inch in transverse diameter, 



so that they are barely visible to the naked eye as single 



;; Except in Dragon-flies and Ephemerae. 



