18 W. H. FURLONGE ON THE PULEX IRRITANS. 



of fresh blood from the first stomach ; but, as before mentioned, 

 ■when the creature has the opportunity of taking in an unlimited 

 supply of food, it has the power of expelling the whole contents of 

 the sac, which then becomes filled with fresh blood. This power of 

 ejecting the contents of the second stomach in whole or in part at 

 the will of the animal, explains the manner in which the female 

 insect is enabled to make provision for the sustenance of the larva, 

 when it emerges from the egg, as originally observed by the late 

 Kichard Beck, by emitting portions of semi-digested food in small 

 drops which immediately coagulate and form the food of the larva 

 when hatched. 



The Respiratory System. — We now pass on to the consideration 

 of the organs of respiration, and I may premise by observing that I 

 know of no creature in which the typical respiratory system of the 

 insecta can be so admirably seen or so conveniently studied as in 

 the Pulex. Mr. Lowne correctly remarked in the course of his 

 observations upon my last paper, that when a living flea is immersed 

 in glycerine and examined by reflected light, its tracheal system 

 appears as if injected with mercury. But I think it may be even 

 more beautifully shown, and certainly more advantageously studied, 

 by transmitted light under the ^in. objective. Selecting a young 

 and transparent specimen, which, for the purpose of observing the 

 tracheal vessels to the best advantage should be kept without food 

 for about 48 hours, in order that it may be compressed somewhat 

 powerfully without injury, the employment of the ^in. objective 

 reveals a structure of extraordinary beauty and wonderful complexity. 

 I have attempted in the accompanying drawing to delineate the 

 general form and course of the main tracheal vessels of the abdo- 

 minal system, but it is simply impossible for the most accomplished 

 and careful artist to do full justice to the subject, and the drawing 

 now shown has no pretensions to be more than a mere sketch, simply 

 intended to illustrate the description I am about to offer. 



The principal portion of the respiratory system of the flea is seen 

 to consist of two main tracheal vessels running along the entire 

 length of the abdomen, just beneath the chitinous envelope on each 

 side, and passing, as will be afterwards shown, into the thorax and 

 head. At the posterior extremities, the upper and lower main 

 tracheal vessels unite and communicate with those remarkable and 

 very large trumpet-mouthed spiracular orifices, described in my 

 previous paper as situated beneath the margins of the plates sur- 



