558 PHILOSOPHICAL TRANSACTIONS. [aNNO I7OO-I. 



great one, which small one had no conveniency of getting out, being at both 

 ends of a pointed form, but chiefly in the hinder part ; his mouth was screwed 

 into the body of the great worm, from whence it seemed to draw its nourish- 

 ment, and by that means to occasion the other's death. 



How these last worms got into the cavities of these tumours, is to me un- 

 known. But we may suppose that the first or great worm is produced from an 

 egg, which some fly has laid on a willow leaf ; and that this worm having 

 gnawed through the vessels of those leaves, a sort of viscous matter issued 

 thence, which intangled the worm, and being dried up together, produced such 

 knobs in the leaves, which inclosed the worms. Now some time after a lesser 

 sort of fly might pitch upon the same knob, and make a hole, and lay its eggs 

 in it, from whence proceeded the above-mentioned little creature, which de- 

 vo red and lived upon the great worm. 



After the knobs had been in the glass tube about 8 days, I opened one of 

 them, and saw that the worm was turned into a tonnekin or aurelia ; I then 

 opened others, and took out 13 or 14 more tonnekins. In some of the said 

 knobs I found those little devouring worms before-mentioned ; I call them de- 

 vouring, because they prey upon a worm at least 50 times larger than them- 

 selves ; they were so far advanced in growth, that without using any more food, 

 they were ready to be changed into flying insects, which I also put into the 

 glass tube. These tonnekins were of a darkish red colour. On opening one of 

 them, I found the worm lying entire as it was, though it had been shut up in 

 its shell above 14 days. 



After some weeks, I perceived certain black flies proceeding from the tonne- 

 kins, the hinder parts of their body being of an oblong figure, and shaped like 

 a hook; the others could not arrive to maturity, but having made a small 

 opening in their pellicles, they just put their heads through, and died. From 

 the same tonnekins proceeded a second sort of fly, that were less than the for- 

 mer, and not so pointed at the end. I saw two of those small worms which used 

 to devour the great ones, endeavouring to shut themselves up into a web : but 

 by reason of the large space they lay in, they could not bring it quite round 

 them, and only made it on one side. But their change happened in so short a 

 time', that I could not make my remarks on it, and as the moths, silk-worms, 

 &c. lie very regularly in a sort of skin or membrane, with their legs and wings 

 after their change, so lay also the horns and feet of these little animals, each in 

 a particular pellicle, but separate from the body, and after the same manner lay 

 tht hinder part of their body, which were shaped much like a hook. These 

 toil ekins, which at first were white, after a few days turned blackish, and at 

 last produced that kind of fly with the above-mentioned instrument, like a hook, 



