Mangan— Ow the Mouth-Farts of some Blattidce. 7 



of the abdominal appendages in Thysanura and Myriopoda. The evidence is 

 on the whole, distinctly favourable to the homology of the palp with the 

 jointed ambulatory thoracic leg in the Insecta, and, consequently, with the 

 endopodite of the typical crustacean appendage. 



The Labium. (Plate III.) 



Authors, with the possible exception of Verhoeff, very generally regard the 

 labium as the fused appendages of the segment coming next to that bearing 

 the maxillae — a segment which, according to Huxley ('77), is represented by 

 the cervical sclerites. Notwithstanding its juxtaposition to the tongue, its 

 parts in the cockroach are distinctly free from, and in no way directly con- 

 nected to, the head-skeleton. 



The cervical sclerites, which we may provisionally regard as belonging to 

 the segment bearing the labium, are eight in number. The two dorsal are 

 triangular, and meet in the middle line ; at the sides are the lateral sclerites 

 {v and u), while the two narrow setiferous bands (t) are the ventral elements. 

 From tc, the largest sclerite, a pair of muscles {S) converge, to be inserted on 

 the epicranial plate. 



The squarish submentum (sm) is the basal piece of the labium, and, despite 

 its relatively large size, is believed to result from the union of the first seg- 

 ments, or cardines, of the constituent appendages. The mentum (me) is much 

 shorter and a little narrower, and its distal border overlaps to some extent 

 the succeeding surface — a point which is not evident when the labium has 

 been removed and mounted. Some regard the mentum as composed of the 

 entire stipites; but it is obvious, I think, to those who believe that the 

 lacinia or galea is a masticatory ridge of the stipes segment, that the mentum 

 contains but portion of the stipites. To me it appears that there is no joint 

 in the maxilla corresponding to the distal articulation of the mentum. If 

 viewed from the back, the remainder of the labium seems to consist of a 

 strongly chitinized piece, with which, on each side, are very distinctly 

 articulated a lacinia {la), a galea (go), and a palp (j9/j of three segments. 

 Moreover, a little distance from the end of the mentum is the furthest point 

 to which fusion of the primitively separate appendages has advanced. Viewed 

 from in front, the cuticle in this region is seen to be thin and flexible, bearing 

 fine scale-like markings, and the galea and lacinia exhibit no jointing with 

 the main part ; while on this side there is decided indication of an additional 

 segment, the palpiger (^J^r). The cuticle of the anterior surface merges on 

 to the hypopharynx, on a level with the distal border of the submentum. 



