THE ANATOMY OF THE ADULT MOSQUITO 101 



which connects the broad-ended cell-mass with the duct ; 

 and if the latter be examined under a good apochromatic 

 lens, it can be distinctly made out that, minute though it be, 

 this chitinous wall of the tube is pierced by spirally arranged 

 minute perforations, each corresponding to the point of 

 origin of a cell. 



In connection with the search for parasitic elements it is 

 well to remember that, there being no connective or other 

 elements to confuse the issue, any other structure than these 

 very characteristic gland cells must necessarily be abnormal. 



Each gland consists of three lobes about three times 

 as long as they are wide, and the three ducts unite at the 

 same point into the right and left salivary ducts ; but 

 these have only a short separate course, and at a point 

 near the base of the pharyngeal bulb, they, in their turn, 

 unite into a common median duct which terminates in the 

 manner already described. The six lobes lie close together 

 on the oesophageal bulb, and together cover the whole 

 of its ventral surface and the greater part of its sides. 

 The only other point requiring notice is that the extra- 

 glandular portion of these ducts is strengthened by a spiral 

 or annular thickening of the chitine, so that they present 

 a close resemblance to a trachea emptied of air ; but there 

 is this difference, that whereas in the trachea the thickening 

 is on the inside of the tube, in the salivary ducts it is 

 distinctly placed on its outer surface. There is no separa- 

 tion or distinction whatever between the salivary and poison 

 glands, which hence are now commonly referred to as the 

 " veneno-salivary " glands. 



Behind the bubar thickening in which it commences, 

 the oesophagus is continued as a simple transparent tube, 

 through the whole length of the thorax, and the only point 

 that requires special notice is that it is not uncommon, 

 in dissecting, to bring away attached to it a pair of delicate 

 bags of air bubbles, the true nature of which will be referred 

 to in the description of the respiratory organs. 



The dissection of the remainder of the digestive apparatus 

 is a simple matter, and the structures that compose it may 

 l)e easily demonstrated in the following manner : — Take a 



