78 ANIMAL PARASITES. 



the anterior truncate and furnished with a flat, round operculum, 

 which, at the margin, passes over into the side walls almost at a 

 right angle, and is let into the rest of the chorion by a furrow 

 which only cuts through its outer strata. The chorion, with 

 which the delicate vitelline memhrane appears to be firmly amal- 

 gamated, is very firm and sir/"* in thickness, homogeneous and 

 structureless, except the operculum, which presents an uneven, 

 finely granular surface, Swammerdamm's little knobs without any 

 particular form, to the number of 10 14. These little knobs are 

 cells with delicate membranes, closely approximated, and which are 

 displaced by the mere pressure of the covering glass and then 

 form a folded mass ; they are about ~" in diameter and have 

 the margin of the operculum free. Even Swammerdamm was 

 acquainted with a white point in the midst of these knobs, which 

 he described as a small hole. This little hole is the micropyle, a 

 perpendicular canal of ^" , which is somewhat dilated externally, 

 and furnished at its margin with a circlet of projecting tubercles, 

 by which the external aspect of the micropyle is rendered stellate. 

 Further from this aperture we also perceive a distinct annular 

 ridge of about '" in diameter. The posterior pole of the egg is 

 truncated, striated by longitudinal folds and ridge-like deposits, 

 and appears to form an adhesive apparatus. 



When the eggs are laid, they stick firmly to the human hair, 

 and are called nits ; in six days they allow the young to escape, 

 and these are ready to lay eggs again at the age of eighteen days. 

 A female lays fifty eggs in all. 



The diagnosis is easy, because the lice creep about upon the 

 head, and their eggs are large enough to betray themselves to 

 the naked eye, especially in dark hair. 



The symptoms which they produce are a troublesome itching 

 upon the skin of the head, which alone they inhabit. Wounding 

 by lice betrays itself by an eruption, on the apex of which there 

 is a blood-red crust, which is produced by scratching off the epi- 

 dermis, which is loosened over a considerable space by reactive 

 phenomena and by the subsequent emission and drying of a few 

 drops of blood. 



Therapeutics. When the hair is otherwise healthy and not 

 too long and thick, careful combing is generally sufficient ; with 

 care this will effect the object in about eight days, as the 

 brood escapes in six days and only begins to lay eggs in eighteen 

 days. But if the hair be very thick, and at the same time long or 



