PEDICULUS HOMINIS. 



483 



for the stomach makes no distinct bag. Is the crop only a reservoir? 

 or is it a preparer of particular food, as in other animals ? I should 

 suspect it is only a reservoir, as I find food in it that does not require 

 being prepared, which is proved by the same food being found equally 

 in both it and the stomach. Therefore it appears that when there is 

 more food than what is immediately necessary, it is thrown into the 

 crop to be used in future. 



There are two salivary glands in the form of two ducts, which take 

 their rise in the abdomen, among the intestines, and which pass up 

 through the abdomen, join the oesophagi [the true gullet and the canal 

 of the crop] and pass with them through the thorax to the head ; at 

 which part they are thrown into convolutions, and there enter the 

 common oesophagus. Whether these are the remains of the silk glands, 

 viz. the glands for forming the chrysalis bag, I do not know, but sup- 

 pose they may be. 



In the large fly each egg is enclosed in its oviduct, and at the outer 

 part of each, a new egg forms, so that as many eggs so many oviducts. 

 The points of the whole are upward and inward, making one plane, 

 touching the crop. Their terminations make also one plane, which is 

 downward and outward, and from each goes a duct to the main one ; 

 but the separate ducts are hardly visible 1 . 



[Order Aptera.] 



The Louse [Pediculus Hominis 2 ~\ . 



Take a louse and starve it, and it becomes almost transparent ; but 

 there is commonly a dark line in the centre, which is the stomach and 

 intestine, having some of the blood digested or reduced to faeces. But 

 let such a louse suck, it will fill itself with blood, and while it is sucking 

 it will throw out at the anus the former contents, which are found to 

 be dry : when it is full, view it in a microscope, and the stomach and 

 intestine are seen contracting and dilating, keeping up a constant 

 motion in the blood ; so that if one were not acquainted with the facts, 

 it would appear to be the heart moving, and disposing of the blood : but 

 their own blood is not red ; it is transparent. How small the vessel 

 must be which they wound ! for there is no mark visible to the naked 

 eye, nor does any blood flow after, as in a leech-bite. 



[Hunt. Preps. Phys. Series, Nos. 2963—2966.] 



[The anatomy of this insect is given by Swammerdam, Biblia Naturae, tab. . ii.' 



2 i2 



