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On the Internal Structure of the Pulex Irritans, 

 By W. H. Furlonge. 



{Read Fehruary 2Srd, 1872.) 



Before entering upon the subject of the second portion of my 

 communication on the Pulex irritans, viz., its internal structure, I 

 think it desirable to state, that I have not been able to resort to 

 actual dissection of the insect, in aid of my observations. In 

 fact, it appears to me, that such extraordinary manipulatory skill 

 would be required to dissect so minute a creature, that any 

 attempt to accomplish such a task, would prove almost abortive, 

 even to the most practised eyes and fingers. Fortunately, how- 

 ever, such is the transparency of the chitinous envelope of 

 the insect, that it is possible to observe every organ, almost as 

 perfectly as if enclosed in glass, even when employing such com- 

 paratively high powers, as the ^in. Nevertheless, I have been 

 obliged to leave wholly untouched some portions of the internal 

 structure of the animal, such, for example, as the nervous system, 

 and several of the glandular organs, and I shall be greatly pleased 

 if other workers, of greater anatomical skill, will shortly fill up the 

 gaps I have left in this investigation. 



The internal structure of the flea may be conveniently described 

 under the following heads : the alimentary and digestive system 

 with the organs pertaining thereto, the respii-atory system, and the 

 reproductive organs. 



1st. — The Alimentary and Digestive System. 



In my previous paper I have stated that I regard the commence- 

 ment of the alimentary canal as a slender fleshy proboscis, perforated 

 by a canal, through which the blood is sucked directly, and very 

 rapidly, into the first stomach by the constant powerful muscular 

 action by which the insect is enabled to dilate its external en- 

 velope. In the course of my investigations I have had occasion 

 to preserve individual insects alive for weeks together, and, there- 

 fore, to feed them, and thus I have had very numerous opportunities 

 of observing the process of imbibition. My method of procedure 

 was to keep the insects in a corked test tube, and when it was 

 desired to feed them, I inverted the tube upon my wrist or forearm. 

 The creatures almost instantly fastened on the flesh, and usually 



