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numerous thin long hairs, forming a kind ol' tnft, (PL XIII. fig. 9). This organ 

 being confined to the male, or at the most slightly indicated in the female, may- 

 be interpreted as serving a sexual purpose. It appears therefore highly probable 

 to us that the fore leg is used by the male in taking hold of the other sex. But 

 as it is reduced to the same degree in both sexes, it may have other functions 

 as well. We do not think that it can be employed when the insect glides through 

 the fur of the host, as the erect bristles of the tibia and tarsus would be a serious 

 hindrance. As the bristles of the femur and those on the side of the tibia 

 (PI. XIII. fig. 6) are directed backwards, i.e. those bristles which come into contact 

 with the hair of the host when the fore legs are tucked away underneath the 

 hollow sides of the prothoras, we believe that the forelegs are kept in this position 

 when the insect moves about. 



Apart from the sensory hairs, the bristles of the body and appendages serve 

 two purposes : protection and adhesion. Firstly, they obviate undue friction with 

 the hair of the host and prevent the hairs from getting in between the joints ; 

 and secondly, they render it practically impossible for the insect to slide backwards 

 through the fur by its own weight and fall off the host. Like fleas, the Polyctenids 

 can only move forward in the fur, the bristle being directed backward, rendering 

 the surface smooth from the frontal side and rough from the anal direction. 

 Many of the long bristles, particularly the bristles of the tibiae, are serai-erect 

 and divergent, and serve as supports for the body by resting on the liairs of 

 the host, in the same way as by means of its numerous branchlets a broken-off 

 twig may remain hanging in a bush. From this point of view the tibiae of 

 the American Polyctenids are interesting, as they bear at the outer edge some 

 exceedingly long and thin bristles, some of which equal the tibia in length. 



The number of abdominal segments is ten in the immature specimens and 

 nine in the adults, the basal segment of the 3'oung apparently disappearing or fusing 

 with the metathorax in the final instar. Apart from the greater or lesser breadth 

 of the abdomen, the species differ as a rule in the number and length of the hairs, 

 and in one case there is also a sexual difference, the males lacking some of the 

 hairs and bristles of the females. 



In order to complete our short survey of the morj)hology we must briefly 

 enter upon a point which is of equal importance for the systematics of the family 

 as for phylogenetic considerations — that is, the question as to the differences 

 between adult and immature specimens. 



We have examined five immature examples belonging to several species, and 

 found them to agree in the following points : The proboscis has the same number 

 of segments and essentially the same structure as in adults of the same or allied 

 species. The elytra are shorter, and, like the pronotura, are devoid of punctures. 

 The bristles of the upper and under sides are fewer in number. The sternal 

 sclerites are less well defined, but the presternum is practically as in the adult, 

 apart from the bristles. Between the mctanotum, which is visible on account 

 of the elytra not being fully developed, and the segment which bears the first 

 abdominal stigma there is a transverse sclerite not noticeable in adults, and 

 presumably representing the true first abdominal tergite. The tarsi consist of 

 two or three segments, and further differ from adult tarsi in the second joint 

 (= division between segments 2 and 3) being situated close to the first in or 

 near the place where the adult tarsus has a pseudo-joint, the third segment being 

 long and undivided. The upper side of the body has no combs or spines, or 



