356 



ORDER III. 



PARASITA* 



The Parasita, so called from their parasitical habits, have but six 

 legs, and are apterous, like the Thysanoura ; but their abdomen is 

 destitute of articulated and moveable appendages. Their organs of 

 vision consist of but four or two simple eyes ; a great portion of 

 their mouth is internal, exhibiting externally either a snout or pro- 

 jecting mammilla containing a retractile sucker, or two membranous 

 and approximated lips with two hooked mandibles. According to 

 Linnaeus, they form but one genus, that of 



Pediculus, Lin. 



Their body is flattened, nearly diaphanous, and divided into twelve 

 or eleven distinct segments, three of which belong to the trunk, each 

 bearing one pair of legs. The first of these segments frequently 

 forms a sort of thorax. The stigmata are very distinct. The 

 antennae are short, equal, composed of five joints, and frequently 

 inserted in a notch. There are one or two small ocelli on each side 

 of the head. The legs are short, and terminated by a very stout 

 nails, or two opposing hooks, which enable these animals to cling 

 with great facility to the hairs of Quadrupeds, or to the feathers of 

 Birds, whose blood they suck, and on whose body they propagate 

 and pass their lives. They attach their ova to these cutaneous ap- 

 pendages. They multiply excessively, and one generation succeeds 

 to another with great rapidity. Particular and unknown causes 

 facilitate their increase to an astonishing degree in the P. humanus, 

 prodvicing in Man what has been termed the morbus pedimdoms, and 

 even in children. These Insects always live on the same Quadrupeds 

 and on the same Birds, or at least on animals of these classes, which 

 have analogous characters and habits. Two species frequently live 

 on the same Bird. Their gait in general is very slow. 

 Some of them — Pedicidea, Leach — such as the 



Pediculus, Deg., 



Or true Lice, have a mouth consisting of a very small tubular 

 mammilla situated at the anterior extremity of the head, in the form 

 of a snout, containing a sucker when at rest. Their tarsi are com- 

 posed of a joint almost equal in size to the tibia, terminated by a very 

 stout nail, folding over a projection, and with this point fulfilling the 

 function of a forceps. Those which I have examined presented but 

 two simple eyes, one on each side. 



* Parasita, Lat. — Anoplura, Leach. 



