4 Proceedings of the Royal Irish Academy. 



ligulate muscle ( V) passes from the base of the plate [z) to the posterior por- 

 tion of the tentorium [ten) . Some muscular fibres, which are inserted very 

 basally on the anterior surface of the tongue, converge to two tendons which 

 pass over the upper surface of the tentorial plate, and take their origin from 

 the posterior edge of its circular aperture. A pair of muscles (not depicted 

 on drawing) pass from the labium, above the mentum, to the region of inser- 

 tion of the muscle V at the base of z. 



The salivary duct {scd) opens to the exterior at the back of the tongue, 

 between it and the labium. At the sides, and somewhat in front of this 

 opening, there are a pair of pit-like depressions, which I take to be salivary 

 receptacles ; the left receptacle {rccp) is seen in fig. 1 . 



The view has been put forward that the hypopharyn.K represents the 

 appendages of a head-segment, while Heymons ('95) entertains the idea that 

 it represents the sterna of the segments which bear the mandibles, maxillse, 

 and labium ; the majority of zoologists, however, regard it as a secondary 

 outgrowth from the mouth region. That it stands in close relation to the 

 mandibles is, perhaps, suggested by the muscles {In) passing from the interior 

 of those jaws to its sides. 



The Maxilla. (Plate II.) 



For descriptive purposes the maxillas are generally considered as composed 

 of a horizontal basal segment, the cardo, succeeded by a vertical segment, the 

 stipes, the latter carrying a galea, lacinia, and palp ; Hansen ('93), however, 

 extending the term 'stipes' to the appendages which it bears. They are placed 

 widely apart, so that the fused second maxillae, or labium, coming between 

 them, meet the root of the tongue. The cardo [car) is an outwardly convex 

 plate, and is distinctly divided into two portions, a strong internal ridge 

 projecting inwards along the line of demarcation. Proximally it articulates 

 with the epicranial plate, and with the lower corner of the chitinous frame 

 which surrounds the occipital foramen ; distally it supports at right angles 

 the stipes {st). The stipes presents a strongly thickened posterior surface, 

 the sclerite lapping round the outer border, and extending for a short 

 distance upon the anterior surface, which elsewhere is covered but by a thin 

 cuticle. Front and back, flexible flaps extend from the inner edges of both 

 cardo and stipes to the head and to the labium, offering, however, no impedi- 

 ment to the free motion of these segments. Near the distal end of the stipes, 

 close to the outer edge, there arises on the anterior surface the five-segmented 

 palp {2)1). A strong setiferous sclerite {sc) at its base suggests a sixth 

 segment. 



