292 OBSERVATIONS ON INSECTS. 



stance, I confined in a close box a slug which, to all 

 appearance, was free from parasites. On opening 

 the box a day or two afterwards, I observed very 

 many crawling about the slug externally, all of 

 which would seem to have proceeded from the pul- 

 monary cavity. On another occasion, I observed 

 these insects running in and out of this cavity at 

 pleasure ; and some which I saw retire into it never 

 reappeared, although I watched the slug narrowly 

 for a considerable time. It is remarkable that the 

 slug appears to suffer no particular inconvenience 

 from these parasites, and even allows them to run in 

 and out of the lateral orifice without betraying the 

 slightest symptoms of irritation. 



Another curious circumstance in the history of 

 these little mites, is the extreme rapidity of their 

 motions. One might have thought that so slimy a 

 ground as the surface of a slug's back would have 

 impeded their progress ; but so far is this from 

 being the case, that they are never to be seen 

 at rest : indeed they run with greater celerity than 

 any other parasites of this tribe I am acquainted 

 with ; these insects, in general, being rather slow in 

 their movements than otherwise. From this circum- 

 stance, it becomes difficult to secure them for exami- 

 nation ; and the more so, from their bodies being of 

 a soft nature, and crushed by the slightest touch. 

 Perhaps the most effectual way is to drop the slug 

 into very weak spirits, sufficient to paralyse the 

 limbs of the parasite, without immediately destroy- 

 ing life. If dropt into plain water, the mites rise to 

 the top, and run about with as much ease and 



