76 AGRICULTURAL EXPERIMENT STATION. 



Dissections and examinations of the internal anatomy can be 

 satisfactorily made with fresh specimens only, as the internal 

 structures of those which have been preserved in alcohol are in 

 such a condition as to be of little or no value except for deter- 

 mining- the development of the ovaries. The dissecting should 

 be done in a weak salt solution. Six tenths of one per cent, is 

 recommended by Berkeley,"^ and if the solution is to be kept, it 

 should be filtered, sterilized, stoppered with cotton and the 

 dropper used should also be sterilized, otherwise the solution will 

 not keep clear. However, tablets are now prepared for making 

 a nonnal salt solution, so that it will be easier to make up a fresh 

 supply when wanted than to save it. In examining the dissections, 

 care should be taken to place a hair or something similar under 

 the edge of the cover slip so that the object will not be pressed 

 out of shape. 



The internal structures, which can be readily found with a 

 little practice, are the alimentary canal with its appendages and 

 ovaries. The other structures — the respiratory, circulatory and 

 nervous organs — will not be readily seen upon ordinary examin- 

 ation, although portions of the nerve cord with g-anglia, and bits 

 of trachea, or air tubes, will sometimes be observed. The ali- 

 mentary canal, beginning in the head at the base of the beak, 

 extends the length of the body. In front is the gullet or oesopha- 

 gus, which extends half way through the thorax to the anterior 

 end of the stomach, at which point three suctorial vesicles are 

 attached, two of them situated in the thorax, while the third or 

 middle one, being longer than the other two, extends backward 

 into the abdomen. Generally they are filled with small air 

 bubbles and thus are more easily seen. The stomach consists of 

 two parts, the narrower portion, situated in the thorax, and the 

 larger, situated in the abdomen, from the posterior end of which 

 the intestine extends to the extremity of the abdomen. At the 

 beginning of the intestine five large, rather short processes are 

 given off, known as the Malphigian tubules, which are supposed 

 to be urinary in function. In the posterior end of the abdomen 

 in the female a pair of ovaries will also be found, situated one 

 on each side. 



To obtain good specimens of the alimentary canal, first re- 

 move the legs and wings — which is aways best to be done in 

 making fresh dissections — then cut off the head, remove the 

 upper surface of the thorax and free the alimentary canal from 

 the remaining portion and in like manner from the abdomen. 



* Laboratory Work with Mosquitoes, by Wm. N. Berkeley, Pediatrics Lab- 

 oratory, 254 West 27th street, New York City. 



