CHAPTER XIV 



THE COMPARATIVE PHYSIOLOGY OF THE 



SALIVARY GLANDS 



While the rest of this book deals exclusively with the salivary 

 glands of mammals, in particular those of man, the cat, dog and 

 rat, in this chapter we will discuss some of the variants in salivary 

 gland function found in other orders. These are of great interest in 

 showing the specialized functions that the glands can undertake, 

 although in most instances little is known of the details of their 

 physiology. 



Different classes of insects showed considerable variation in the 

 degree of organization of their salivary glands ranging from quite 

 rudimentary sacs to elaborate organs in many of the higher insects. 

 Baptist (1942) gives a good account of the salivary glands of 

 Heteroptera. In Notonecta glauca L. the glands are characterized 

 by large cells with prominent granules and vacuoles. The glands 

 are innervated by a nervous plexus receiving a glandular nerve 

 from the hypocerebral ganglion of the stomato-gastric system. The 

 gland cells discharge their granules during activity. In other mem- 

 bers of the heteroptera, vesicular glands are found. The secretion 

 from the gland cells is discharged into a large central storage cavity. 

 These gland cells contain no zymogen granules but there are small 

 dense masses of "reserve material" in the basal parts of the cells. 



The silk glands of lepidoptera larvae are specialized salivary 

 glands ; in other orders silk is produced by other glands, for instance 

 in Arachnids by ventral abdominal glands, in Embioptera glands 

 situated in the front feet and in Coleoptera by glands in the Mal- 

 pighian tube or accessory genital tubes (Lesperon, 1937). In Seri- 

 caria mori the silk glands are two long tubes that unite in the mouth 

 to form a common tube into which two accessory multilobed 

 glands (the glands of Lyonnet) add their secretion. These secretions 

 are passed along the specialized mouth parts (the silk press) in 

 which the two cylindrical filaments of silk are fabricated into a 

 single plaited ribbon. The tubular silk glands are lined by a single 

 layer of cells which show differences between the most proximal 

 region in which the fibres of silk fibroin are probably made in cells 



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