parasitical on Slugs. 



539 



of which would seem to have proceeded from the pulmonary 

 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, as 

 Dr. Shaw observes, that the slug appears to suffer no parti- 

 cular 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 insects 

 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 rather 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 with which I am acquainted; these 

 insects, in general, being rather slow in their movements than 

 otherwise. From this circumstance, it becomes a difficult 

 matter to secure them for examination, and the more so, their 

 bodies being of a soft nature, and crushed by the slightest 

 touch. My first attempt consisted in dropping the slug into 

 water ; but I was rather surprised to find that the ^'cari, 

 although immersed, rose instantly to the top, and ran about 

 with as much celerity upon the surface of the fluid as upon 

 the slug itself. I afterwards tried the same experiment with 



weak spirits, which was at- 

 tended by better success; the 

 spirits having the effect of 

 paralysing the limbs of the 

 parasite, without immediately 

 destroying life. It was, ac- 

 cordingly, in this manner 

 that I was enabled to make 

 the accompanying drawing 

 (J/g, 109.)? and to note down 

 the description of this in- 

 sect, to which I shall now 

 proceed. 



Although this little ^"ca- 



fl, A very highly magnified representation of this yUS is UOt altogether UCW, I 

 insect. ^ /? ^ v i 



b. The terminal joint of the foot, still more en- am UOt awarC that it UaS CVCr 



^^^^^^' received a name, or had its 



distinguishing characters accurately defined. It will not asso- 

 ciate well with any of Lamarck's genera; and I am unacquainted 

 with a more recent arrangement of this much-neglected tribe. 

 It seems to bear some distant affinity to Erythrse^us, which it 



