68o 



THE POPULAR SCIENCE MONTHLY. 



distill into the wound a liquid venom which occasions the irritation 

 that follows the bite. Fig, 11 shows the form of the larva and nymph 

 of this insect. The former will be recognized as the little " wriggler " 

 that may be seen in such numbers in stagnant water in summer. For- 

 tunately, these insects are harmless until they acquire wings, and after 

 that their life is a short one ; but, unfortunately, they breed at an enor- 

 mous rate, and thus maintain the supply, to the infinite annoyance of 

 man and other tender-skinned animals. 



Another blood-sucking parasite of both man and beast, whose stay- 

 ing tendencies are proverbial, is the louse. Fig. 12 represents the 

 species that inhabits the head of man. The mouth of this insect con^ 

 sists of a sucker contained in a sheath, without articulations. It is 

 armed at the point with retractile hooks, within which are four bristles 



Fig. 12. Louse of the 

 Head. 



Fig. 13. Louse op the Head. 

 2, 3, Sucker. 



Fig. 14. Louse op the Head, 

 Claw. 



that aid in breaking through the skin. They have climbing feet ter- 

 minated by pincers, with which they maintain their hold on the hairs. 

 The sucker and claw are illustrated in Figs. 13 and 14. The nits, or 

 eggs, hatch in five or six days after they are laid, and in eighteen days 

 more the creature is able to reproduce its kind. Leeuwenhoek calcu- 

 lated that two females might become the grandmothers of 10,000 lice 

 in eight weeks. 



A not less annoying parasite that lives on the blood of man and 

 the higher animals is the flea. Both male and female get their living 

 in this way, and even the larvae are supplied from the same sources by 

 the mother, who sucks for herself first, and then divides with her 

 young ones. The ordinary flea [Pulex irritans, Fig. 15) is common 

 in both Europe and North America. It may be called a fly without 

 wings, and, together with others of its kind, forms a distinct family 

 under the name Pulicidm. The four principal species are Pulex irri- 

 tans of man, Pulex canis of the dog, Pulex musculus of the mouse, 

 and Pulex vespertilionis of the bat. Great numbers of human fleas, 

 half as large as the common fly, are found in summer on the sandy 



