as affecting Domesticated Animals. 35 



segments, including the liead. These gradually increase in 

 size towards the caudal extremity of the creature, reaching 

 their fullest dimensions at about the tenth segment, from 

 which thoy again diminish. Although the larva is not fur- 

 nished with legs, it is nevertheless remarkably active in its 

 movements, which are crawling or worm-like. The head is 

 surmounted by two very small antennae. The mandibles are 

 well developed, but their precise arrangement does not admit 

 of being clearly defined. No eyes can be detected. Each seg- 

 ment below the head is beset with a few stiff hairs, the number 

 and size of which also increase towards the caudal end ot the 

 larva. On the edge of the last segment but one the hairs are so 

 long and thickly set as to form a kind of fringe, which often'^pro- 

 jects beyond the booklets that are here developed. A similar 

 arrangement of them is also to be observed, but in a less degree, 

 upon the last four or five segments. Besides this peculiarity, 

 the extreme end of the last segment is furnished with a tuft of 

 very fine hair, and it gives origin also to the two small booklets 

 previously alluded to. 



Fig. 1. 



Ovum and Larva of Dog-Flea. Magnified. 



It is thought by some naturalists that the larva of each variety of 

 flea, besides inhabiting the skin of the animal to which it especially 

 belongs, often travels to other mammals or birds, obtaining from 

 them a supply of food suited to its rapid growth and development. 

 According to Rymer Jones, the larva of the Pulex irritans attains 

 its full size in about twelve days subsequently to quitting the eg^., 

 when it forms for itself a small cocoon, after the manner of the 

 silk-worm, and changes into a pupa. Whatever the fact may be 

 with reference to the larva of this flea, we can take upon our- 

 selves to say that the larva of the Pulex Canis often lives double 

 this time before the change is effected. The period Avhich 

 elapses before the imarjo bursts forth is said by Newman 

 and others to range from eleven to sixteen days, a statement 

 which our observations tend to confirm. 



The Pulex Canis. — Firstly, it is necessary to remark, that as 

 the form of the flea is modified in each individual animal whose 

 body it inhabits, the flea of the dog can be easily distinguished 

 from any other by a microscopical examination. The chief 



D 2 



