THE FLEA. 631 



wings, in the form of horny plates on both sides of the 

 thoracic segments. Its mouth consists of a pair of sword- 

 shaped mandibles, finely -serrated ; these, with a sharp, 

 penetrating needle-like organ, constitute the formidable 

 weapons with which it pierces through the skin. 



The neck is long, the body covered over with scales, the 

 edges of which are set with short spikes or hairs ; from its 

 "head project a pair of antennae, feelers or horns, a pro- 

 boscis, which forms a sheath to the pair of lance-shaped 

 weapons. On each side of the head a large compound eye 

 is placed. It has six many-jointed powerful legs, termi- 

 nating in two-hooked claws ; a pair of long hind legs are 

 kept folded up when the insect is at rest, which in the 

 act of jumping it suddenly straightens out, at the same 

 time exhausting all its muscular force in the effort. The 

 female Plea, fig. 287, lays a great number of eggs, sticking 

 them together with a glutinous secretion j the Plea infest- 

 ing the dog or cat glues its eggs fast to the roots of the' 

 hairs ; in four days' time the eggs are hatched, and a small 

 white larva or grub is seen crawling about, and feeding 

 most actively. No. 4 (fig. 289) is a magnified view of one, 

 covered with short hairs, doubtless for the purpose of 

 preventing its dislodgment. After remaining in this 

 state about nine or ten days,, it assumes the pupa form ; 

 this it retains four days ; and in nine days more it be 

 comes a perfect Flea. The head of the Flea found in the 

 oat (No. 3, fig. 289) somewhat differs in form from that 

 of the species infesting the human being. Its jaws are 

 furnished with more formidable-looking mandibles, and 

 from between the first and second joints behind the head 

 short strong spines project. 



Arachnida. The animals forming the class Araclmida 

 include spiders and their allies, most of which are looked 

 upon with disgust and aversion by the generality of man- 

 kind. Arachnida are divided into two orders, Trachearia 

 and Pulmonaria. The first includes the Acaridce or 

 Mites, in which we find tracheae, as in insects, but no 

 distinct vascular apparatus : in the second, spiders and 

 ccorpions are included, and these have a pulmonary cavity, 

 and a well-developed circulatory system. The above are 

 distinguished from Podopthalmia or Arthropoda by their 



