106 THE PHILOSOPHY 



a thread ; but thofe of the male are beautifully feathered. 

 The worms or caterpillars of this genus are commonly found 

 in ftagnant waters. The gnats generally frequent woods and 

 marlhy places. The females, in particular, are very trouble- 

 fome, and fting feverely. The feet of the hippobofca or horfe- 

 Jly, are armed with a number of nails or crotchets. In fome 

 fpecies, the wings crofs each other •, in others, they are 

 open. The horfe -flies frequent woods and marfhy grounds, 

 and are extremely incommodious to birds and quadrupeds, 

 whofe blood is the only food of thefe infedts. 



The feventh order of infedls Linnaeus denominates aptera, 

 becaufe neither males nor females are furniflied with wings. 

 This order comprehends thirteen genera, and a great num- 

 ber of fpecies, many of which are very ofFenlive and noxious 

 to the human fpecies. The pediculus, or loufe, has fix legs, 

 two prominent eyes, and its mouth contains a fling or fucker, 

 by which it extracts blood and other juices from the bodies 

 of animals. Though almoft every different animal is infefled 

 with a peculiar fpecies of lice, fpecific characters of very few 

 of them have hitherto been afcertained. Lice are of various 

 forms. Some of them are oval, others oblong, and others 

 long and flender. They are oviparous animals, and their 

 eggs are large in proportion to the fize of their bodies. Be- 

 fore they arrive at maturity, they change their fkin feveral 

 times. They are fuppofed to be hermaphrodites. This cir- 

 cumflance, if true, may partly account for their prodigious 

 multiplication. Swammerdam, who dllTedled a great num- 

 ber, afTures us, that he never found one without an ovary, 

 nor ever difcovered the organs peculiar to the male fex. If 

 this flrufture be univerfal, the loufe is an hermaphrodite of 

 a very peculiar kind ; becaufe it mufl be capable of foecun- 

 dating itfelf. Several fpecies of worms are hermaphrodites ; 

 but, inflead of foecunding themfelves, they are obliged to im- 

 pregnate each other. The puleKy orjleay has likewife fix legs, 



