8 Transactions of the 



a larva, destined to revel on the fatty matter by wliicli it 

 finds itself surrounded. Nor is this all : the parasites are 

 themselves liable to have their progeny pierced and de- 

 voured by other parasites, even to the third degree. Thus, 

 the common plant-louse or Aphis^ which extracts the juice 

 from so many of our flowers and vegetables, is constantly 

 attacked by various species of a parasite named Aphidius, 

 wich is in its turn preyed upon by a third enemy, an 

 Asaphes ; the Aphis being pierced and used as a nest by the 

 Aphidius, and the latter, while still inside the Aphis, being 

 treated in the same manner by the Asaphes ! So that, after 

 all, there is no exaggeration in Professor Daubeny's well 

 known jeu de mot : 



Great fleas have little fleas upon their backs, to bite 'em ; 

 And little fleas have lesser fleas ; and so ad infinitum ! 



Few persons, whether strictly entomologists or not, but 

 must have noticed the swarms of lice (as they are usually 

 called, although in fact belonging to the Acari, or mites), 

 known as Gamasus coleoptratorum, which infest the common 

 dor beetle {Geotrupes stercorarius) , whom we so often, on a warm 

 summer's evening, hear ' droning ' through the still air, or, 

 it may be, feel, as it knocks against our hat. A still more 

 curious parasite, though nearly related to the last, is JJropoda 

 vegetans — (like most of these tiny organisms, it has no native 

 name). I found sj)ecimens of the JJropoda a short time ago, 

 attached to the under surface of a beetle {Hister unicolor). 

 Parasites generally trust to their claws for a firm foothold, 

 but Uropoda is gifted with the power of throwing out a 

 veritable cable from near the apex of its abdomen, by which 

 it moors itself to the beetle, just as a ship in the Arctic Seas 

 is often moored to an ice floe. The tiny cable is apparently 

 of the same substance as a single strand of the ' byssus ' of a 

 mollusc, and is so strong and elastic as to make it a matter of 

 some little difficulty to detach the parasite. I find th^t 

 Curtis, the well-known entomologist, figures and describes 

 another species of Uropoda, which he found fixed to the back 

 of a click beetle {Elater), and which he na.jn.ed -U. ^(■mMlica, 

 whose structure is even more curious than that of U. vege- 

 tans, for the c'able by which it is moored issues from the 

 middle of its back; it then makes a curve or arch, and 

 finally glues itself on to the hard wing-case of the unfor- 

 tunate Elater. 



There are other parasites which do not themselves prey 

 upon insects (at least not in their perfect condition), but 



