( 5fi8 ) 



some species have three and others four segments, the first segment being always 

 very short ; of. PI. XII.— XIV. figs. 2. 4. 0. 11. and te.xt-fig. 1. The proboscis is 

 rather soft, and the first and second segmeuts, sometimes also the third, are more 

 or less open on the anterior side, while the end-segment, which is longer than the 

 preceding one, bears a mesial groove on that side, bnt does not appear to be open. 

 The slit in the first and second segments is not covered by an npjier lip, as in the 

 Jlhijiichota. We have moved the proboscis freely, but failed, either by pressure 

 or bending, to find an organ which might be homologous to the labrum, aud we 

 consider it possible that the so-called clipens really is homologous with the labrum. 

 However, transverse sections may reveal the presence of a remnant of this organ. 

 All the segments of the i)roboscis bear short hairs, those on the last one being fairly 

 numerous and more or less symmetrical in position. This segment, moreover, is 

 provided at the apex with a number of short papillae, and its length and shape is 

 by no means the same in the various species. 



The proboscis is carried with the tip pointing backwards, as in a bug, and there 

 is a deep mesial groove on the head for its reception (PI. XII. fig. •.'. 4i, the raised 

 edges of this groove, some hairs placed on these edges, and the spines of the 

 comb presumably preventing friction with the hairs of the host when the insect 

 dives into the fur. 



The upper side of the head is divideil iuto a flat or depressed central portion 

 and the depressed sides. The central portion is anteriorly parallel with the hind 

 margin of the clipeus, or very nearly, aud its lateral edge is more or less elevate, 

 cariniform and continued backwards, being accompanied in adult specimens by 

 a suture, at the outer side of which there is a row of bristles. The raised edge of 

 the central area serves in most Old-World species a distinct purpose in connection 

 with the lateral depression. As indicated in fig. 3 of PI. XII., the antenna, when at 

 rest, lies on the up(ier side of the head in the groove bounded by the carina. The 

 suture which e.xtends, on the upper side, from the point whore the lateral deiiression 

 commences, corresponds most probably to the suture which is situated between the 

 antennae in many other insects, separating the frons from the verte.x. 



While in most species the head is more or less closely applied to the prothora.x 

 (cf. PI. XIII. and XIV. fig. .3. y. 10), there is sometimes a distinct neck between 

 them (PI. XII. fig. 1. 3), in the latter case the angles of the head being more 

 obtuse than in the former. It is very interesting to note that the posterior 

 angles bear a long bristle above as well as below in the species with a neck, 

 while such bristles are absent in the other species. Bristles placed in this way 

 in front of a gap or open joint are met with posteriorly on the prouotum of the 

 Pohjctenidae and in some cases also on the sides of the elytra. They are a feature 

 common to many ectoparasites living in fur, and have evidently the function of 

 warding off hairs which otherwise might get into the joints. 



The difference which exists in tlie shape of the frons and the number and 

 jiosition of the bristles is sufficiently apparent from our figures, aud does not reipiirc 

 further comment ; but we should like to draw attention to a small character which 

 is only present in some nearly related Old-World forms aud lias been overlooked. 

 This is a row of exceedingly small spines placed on each side of the head in front 

 of the comb (PI. XIII. fig. 5. »). We mention this character especially, liecanse 

 we have here one of the very numerous instances where apparently insignificant 

 distinctions are surprisingly constant outward expressions of true relationship. 



As said above, the under surface of the head is elevated at each side of the 



