1921] Crampton — SuperTinguc' or Paraglossa' of Insects 87 



modifications of these ril)-lil\e or ridge-like structures in insects, 

 and it is also possible that certain of these structures may be the 

 precursors of portions of the tentorium of insects, although I have 

 not been able to determine this point as yet. 



The pharyngeal ridge, "pc", of Fig. 3, etc., appears to represent 

 a portion of the sterna of the mouthpart segments, which are C[uite 

 broad in Fig. 4; and the lingua is not developed in the lower Crus- 

 tacea. In Mysis (Fig. 4) the paragnaths, "pg", are borne at the 

 anterior margin of the sternite, "m\s", of the first maxillary seg- 

 ment; and in the lower Crustacea, the paragnaths appear to be 

 more closely associated with the maxillula? or first maxillae, than 

 they are with the mandibles, thus indicating that the paragnaths 

 may represent detached loljes of the first maxilla?. 



In Squilla (Fig. 6), the paragnaths, "pg", are attached to the 

 basal portions of the maxillula? or first maxill;^, "mx", and in the 

 very primitive crustacean Apus (Fig. 7) both paragnaths, "pg", 

 and maxillulse, "mx", arise from the same basal lamina, "bl", which 

 projects internally beneath the body wall. The paragnaths and 

 maxillulse in Fig. 7 are bent over backward (instead of being repre- 

 sented in their normal upright position, as in Fig. G), in order 

 to show that Ijoth paragnaths and maxilluls are borne on the same 

 basal lamina. The fact that both paragnaths and maxillulge arise 

 from the same basal lamina in such primitive forms as Apus, would 

 indicate that the paragnaths of higher Crustacea are merely de- 

 tached lobes of the maxillulge, possibly corresponding to the endites 

 or gnathobase-like structures of the trunk limbs of Apus; and in 

 the higher Crustacea, these paragnathal lobes become more or less 

 separated from the remainder of the first maxillas (maxillula?), and 

 become somewhat more closely associated with the mandibles, as a 

 secondary modification. 



I do not know of any instance in which the paragnaths are situ- 

 ated in front of the mandi1)les, so that the metastoma, "mts", of 

 the trilobite Triartlirns (Fig. 10), which is situated in front of 

 the bases of the so-called mandibular appendages, ^^md", (only the 

 tips of the basal segments of these are shown in the figure) and 

 occupies a position between the bases of tlie so-called second an- 

 tennae, "at", is situated too far forward in the head region, to 



