VOL. XIII.] PHILOSOPHICAL TRANSACTIONS. 583 



these before named filaments, and some threads without indentings which I 

 conceived might be vessels. 



I also with much trouble took out the testicles of a flea, and placed them be- 

 fore my microscope, and drew out the figure as well as I could, as fig. 14, 

 ABC D is the testicle, AF and DE are the vasa deferentia. When the testicles 

 were first taken out they were of a dark colour, but in less than -5V o^ ^ minute 

 their moisture was evaporated, and then they became crumpled, which I have 

 here represented as well as I could. 



I also searched for the vessels having as it were rings about them, and am 

 satisfied they cannot be air vessels, but rather arteries; for I saw them not only 

 encompass the guts, but spread over and among the eggs. The sting or snout 

 of the flea, or rather the sheath in which it is kept, had teeth on each side like 

 a saw ; and may not unfitly be compared to a quill that is split ragged. When 

 the sting is enclosed in the sheath, the teeth on each side go between each 

 other. The length of this sheath is about 3 diameters of the thickness of a 

 hair, 



I have made many attempts the last autumn, to find out in what time the 

 worm coming from the egg of a flea, would become a full grown flea. The 

 eggs of a flea kept in a warm place, were hatched in 4 days, and became worms, 

 which I endeavoured to bring up, but notwithstanding all my endeavours I could 

 keep them no longer alive than 11 days. When I placed about the half of a 

 small fly in the glass by the worms for their food ; the part of the fly caused 

 such a steam on the glass that the worms being hairy were entangled in the 

 moisture, and remained immovable till they died. When the worms were 12 

 days old, they were about the length of 4 eggs, and the thickness of one. 

 Since I could bring lip no worms, I took some which I thought had attained 

 their full growth, and observed the same to spend 8 or 10 days in spinning their 

 web, and then they stripped off their skin and became nymphae. These 

 nymphae I saw move on the 4th day, though they were clear and white : on 

 the 6th they were red about the head: on the iOth they broke their case, which 

 was a very thin skin, and leaped into the glass, living there without food for the 

 space of 7 days. 



I also took some flesh from the breast of a louse, and found the flesh threads 

 of the same make as those of the flea. I took also the flesh from the feet of a 

 gnat, and found that of the same make with the former. But perceiving the 

 legs and body of the gnat to be furnished with ver}' fine feathers, I have caused 

 them to be drawn as fig. ) 5, pi. 13. The wing also of the gnat being adorned 

 with feathers, I have drawn that too, as fig. 16, which is a wing as it appears 

 to the naked eye. Fig. 17, ABC is the same represented in a larger propor- 



