450 E. A. MINCHIN ON SOME DETAILS IN THE ANATOMY OF 



II. The Salivary Glands. 



Having occasion to dissect some flea-larvae, I was struck by 

 the fact that the salivary glands of the larva differ greatly, both 

 in size and in complication of parts, from those of the adult flea. 

 I will begin with the adult, in which the glands are both smaller 

 and simpler in structure. 



In the adult flea the salivary glands lie in the abdomen, right 

 and left of the stomach, in the form of two tiny pouches on each 

 side (PI. 27, B and C). Each pouch consists of large glandular 

 cells, which tend to stain very opaquely and have large nuclei. 

 The two pouches of each side give off each a short duct, and these 

 two ducts unite into a long duct running forwards on the side of 

 the body to the anterior thoracic region, where the two ducts from 

 the two sides of the body unite into a common salivary duct, which 

 runs forwards to open, doubtless, into the hypopharynx, as in 

 other insects. The paired salivary ducts have a very character- 

 istic appearance, being lined by a chitinous cuticle which shows 

 internally a system of rather irregular transverse thickenings. 

 This appearance is seen from the point where the ducts issue 

 from the glands up to a short distance from the spot where the 

 paired ducts unite to form the common salivary, duct ; the 

 structure of the ducts recalls to some extent that of a tracheal 

 tube, but the transverse thickenings are not so perfectly regular 

 as in the tracheae. At the point of union of the right and left 

 salivary ducts, however, there is a Y-piece in which the duct 

 diminishes in calibre to about half, and has no transverse 

 thickenings. External to the chitinous lining, the duct is 

 covered by a delicate layer of flat epithelium, which does not 

 show distinct cell-outlines, but has the appearance of a plas- 

 modial or syncytial layer of protoplasm with scattered nuclei. 



The salivary gland of the adult flea, on account of its small 

 size, is not so easy to dissect out ; the glands of the female are 

 slightly larger than those of the male. On the other hand, the 

 salivary glands of the larva, which are plainly visible through 

 the body-wall of the living insect, are very easily dissected out. 

 All that is necessary is to decapitate the larva in such a way as 

 to cut off the first or first two thoracic segments, together with 

 the head, and then to press with the flat of a dissecting needle 

 gently along the body from behind forwards, so as to squeeze out 



