ARACHNID A. 157 



into a common vagina, into which two seminal receptacles open ; genital pore 

 on ventral surface between penultimate and last segment. Its lower surface 

 forms a transverse ridge. Copulation by beneath J . Eggs pyriform, ^"'; 

 in six days young escape ; a louse fifteen days old can lay. 9 lays fifty eggs. 



Two 9 might become progenitors of 10,000 lice in eight weeks ; a single 

 generation may furnish 2500 lice, the third 125,000. (Leuwenhoek.) 



P. vestimenti. Body louse pretty near preceding. Head exserted, elon- 

 gated in second joint ; antennae elongated ; thorax divided into segments ; 

 dirty white, blacker on margins; principal distinctions between body and 

 head louse pertaining to size. 



Phthirius pubis. Fiddle-shaped head ; prominent eyes ; antennae five 

 joints. 



Habitat. Pubis, hairs of breast, eyebrows, eyelashes. 



Schultz regards lice beneficial ; couriers cherish them, to place them under 

 the prepuce of their horses to excite animation. 



(Pyrcthrum caucaseum, Persian insect powder.) 



AEACHNIDA. 



i ** 



SARCOPTES. Body circular, indented towards centre and obtuse poste- 

 riorly, soft, shiny, slightly transparent, of a whitish color. Dorsal surface 

 convex, ventral less so. Margin slightly undulating, and the surface of ab- 

 domen is marked by more or less parallel, irregular, but curved lines or 

 ridges. Rostrum anterior and straight, somewhat oval, obtuse, two setae at 

 base. Limbs eight in number, two pairs in front, and two placed farther 

 back. Limbs short, conical, distinctly jointed and furnished with hair-like 

 processes. The two anterior pair arise from the thorax ; they have thighs 

 divergent ; the feet terminate in slender, straight, rigid, setae, tubular segment 

 provided at its extremity with a sucker. The four posterior feet pertain to 

 the abdomen ; they terminate in a long, curved, pointed thread, without 

 sucker. The body of the insect has a few hair-like processes scattered here 

 and there, and on its dorsal surface are three kinds of horny appendages or 

 spires ; the first fourteen in number are arranged symmetrically on its central 

 and posterior parts, of a conical form, are traversed by a canal, and furnished 

 with a dilatation or basal follicle ; the second are smaller, and placed near 

 the first ; the third are still more minute ; they are arranged in concentric 

 lines, have no canal, and resemble conical-pointed tubercles. 



The parts about the mouth are surrounded at their commencement by a 

 thin sinuous margin, portions of which extend as far as the organs them- 

 selves. These are as follows : 1st. A pair of strong mandibles, carrying 

 toward tlicir extremity and on their upper side a small movable hook ; this 



