16 W. H. FURLONGE ON THE PULEX IRRITANS. 



contents of the sac are kept in a state of constant motion, tliougli 

 much less violently than those of the first stomach. 



The Rectal Papillce. — Within the intestinal sac are suspended 

 six curious conical teat-like organs, shown in Fig. 3. These organs 

 will be at once recognised by those who are familiar with Mr. 

 Lowne's work on the " Blow-fly," as the rectal papillas, or urinary 

 organs of the insect. I must, indeed, candidly say, that but for Mr. 

 Lowne's observations, it is very possible that the existence of these 

 organs in the flea would have escaped my notice, as, owing to the 

 generally dark colour of the semi-digested contents of the sac, these 

 organs are not very readily discernible. When one knows what to 

 look for, however, and where to seek for them, they can generally be 

 made out very distinctly after a little patient focussing. The rectal 

 papillae are then seen to be glandular organs, composed of a soft 

 fleshy substance of a light yellow colour, having the form of elon- 

 gated cones, the bases of which are flat or very slightly rounded. 

 Into the centre of the base of eacK. of the papillae there enters a 

 small tracheal tube which ]3asses nearly to the extremity of the organ, 

 where it bifurcates and turns backwards, terminating in very 

 numerous and exceedingly minute fibrils, which permeate the entire 

 substance of the organ. Similar delicate fibrils are also given off 

 laterally from the main tracheal filaments in its course through the 

 organ, radiating from the centre to the circumference, and ramify- 

 ing in all directions throughout its structure. The external sur- 

 faces of the papillae appear to be perfectly smooth, and 1 have been 

 unable to make out the existence of any pores or orifices, except 

 perhaps close to the extremities, where the surface seems irregular 

 or warty, and I fancy that on one occasion, when examining a 

 specimen under peculiarly favourable conditions, I was enabled to 

 make out, with the iin. objective, about 10 or 12 orifices at the 

 conical extremities of each of the papillae, and, in point of fact, 

 there can be no doubt that some such orifices must exist whether I 

 have been able really to -see them or not. The tracheal vessels 

 which supply the six papillee all spring from one tracheal tube ex- 

 ternal to the intestinal sac, the branches from which pass through 

 its walls and serve to sujDport the papillse as they hang freely sus- 

 pended within the sac. It is very interesting to watch the constant 

 movements of these long conical finger-like papillae crossing and 

 gliding over each other as the walls of the sac are pulled to one 

 side or the other by the external muscles. 



