PEDICULUS CAPITIS. 77 



change according to the hair ; all the segments are blapkish on 

 the margins. In the human louse I have always found the same 

 transverse ridges on the inner surface of the belly, which are seen 

 in Trichodectes. All the feet are similar. The last tarsal joint 

 bears a large claw on its outside, and on its inside two straight, 

 thick, horny stumps, and a large bristle. The oasophagus is 

 short ; the longish stomach has two csecal appendages. The 

 small intestine is only slightly bent into the form of an S, receives 

 four urinary vessels at its extremity and passes over into the 

 pyriform large intestine. The most essential points as regards 

 the sexual relations are as follows : 



The males are fewer in number than the females, their last 

 abdominal segment is prominent and rounded off, furnished on 

 its dorsal surface with a valvular opening beset with an abundance 

 of asperities, which serves at the same time as an anal opening and 

 porus genitalis. There are two pairs of testes and a simple wedge- 

 shaped penis, which, placed with its base inwards and its apex 

 outwards, opens upon the back. This organ is described by cer- 

 tain authors, as a strong muscular member ; to me it appears to 

 form a hollow chitinous canal, the lateral walls of which are stif- 

 fened and coloured brown by a strong deposition of the chitine- 

 mass, whilst the bottom of the channel is formed of thinner, whiter 

 chitine. The seminal structures are as usual, for example such 

 as are figured for the Trematoda, but I have never with certainty 

 found active, isolated filaments in the testes, but more commonly 

 the stellate bundles. 



The females, which are more numerous and larger, appear 

 deeply notched at the apex of the last abdominal segment and, as 

 it were, with two lobes, between which is the anal aperture, which 

 is surrounded by numerous hairs. The two ovaries consist of 

 five tubes each, collecting into two oviducts and a common vagina, 

 into which two seminal receptacles open. The vaginal orifice is 

 situated on the ventral surface, between the penultimate and last 

 segments. Its lower surface forms a transverse ridge, which is 

 extended in an arched form across the body, and is beset with 

 small digitate asperities, arranged in four to six parallel rows, and 

 their vicinity with small, horny, warty eminences. Hence copu- 

 lation can only take place, by the female mounting upon the 

 male. 



The eggs of the common head-louse, according to R. Leuckart, 

 are pyriform and very large, about J'". The posterior pole is pointed, 



