a supposed CEstrus Hominis or Gad-Fly. 287 



accoid upon the cabin-floor, witli a noise resembling tha 

 which a pebble would make on falling on the ground. It kept 

 moving and turning about for some time, like an earth-worm, 

 but, ere long, shrunk into nearly half its previous size. The 

 atmosphere was at this time cool, the ship being within a week's 

 sail of Greenock. The insect lived for three days, and was 

 then put into spirits, after which it shrunk still more. Calcu- 

 lating from the period at which the itching was first felt, it had 

 lived in Killock's arm, in the larva state, for about six weeks. 

 The wound healed readily, leaving externally the appearance of 

 a small scar. 



In the 12th edition of the Sy sterna Naturae there is no men- 

 tion of this insect. Graelin, however, says, that it dwells be- 

 neath the skin of the abdomen nix months, penetrating deeper 

 if it be disturbed, and becoming so dangerous as sometimes to 

 occasion death. In Dr Turton's General System of' Nature.^ 

 there is the following notice of this insect, or of one of which 

 the habits are similar. " CEstrus hominis. Body entirely 

 brown. Inhabits South America, Linne, ap. Pall, Nord. Beytr. 

 p. 157. Deposites its eggs under the skin, on the bellies of the 

 natives ; the larva, if it be disturbed, penetrates deeper, and 

 produces an ulcer which frequently becomes fatal." 



We are informed that Killock, previous to this attack, while 

 at work, usually wore his shirt-sleeves rolled up above his el- 

 bows ; and that, while in George Town, Demerara, he gene- 

 rally slept on deck. It is easy then to suppose, that the CEstrus 

 or parent fly had availed itself of a proper opportunity to deix)- 

 site its egg upon his arm, probably by a slight puncture of the 

 skin, by means of the ovipositor with which it is furnished. 

 When the larva had attained its full size, it dropped out, in- 

 stinctively searching for a covering of natural earth, in which 

 to undergo the intermediate state of pupa, which it is des- 

 tined to assume for a time before it becomes a winged insect. 

 The instinct of the parent, however admirable under ordinary 

 circumstances, was of course insufficient to provide against the 

 accident of Killock's being a seafaring man, — and the larva 

 could not have attained the perfect state, for want of the pro- 

 per nidus in which the pupa is accustomed to repose. Had a 

 flower-pot containing earth been on board the vessel, the dif- 



