﻿TRÄGÅRDH, CONTRIBUTIONS TO THAUMATOXENA. 9 



If we compare Wandollecks' Fig. 13, Pl. 26 with my 

 textfig. 4 we notice at once, that the only essential difference 

 is, that in Thaumatoxena the lateral edges of the labrum are 

 curved more towards each other and more upwards so as to 

 coalesce with the ventral surface of the labrum, while in the 

 Stetkopathidce they are free. The consequence of this is that 

 in the latter the labial cavity is far larger than in Thauma- 

 toxena, as the textfigs. 5 and 6 show, which represent trans- 

 verse sections through both. 



Furthermore in Thaumatoxena the two chitinous bars 

 coalesce with the roof of the labrum, while in the Stetho- 

 jMthidce they are free. Besides these there are in the latter 

 other accessory complicated structures very different in the 

 three genera. 



Textfig. 5. Textfig. 6. 



Textfig. 5. Transversal section through the labrxim of CJionocephalus 

 dor salts. 



Textfig. 6. Transversal section through the labrura of Thaumatoxena. 

 ep, epipharynx. 



Breddin & BÖRNER (1. C. p. 85) describe the two chiti- 

 nous bars with the furrow between them and interpret it as 

 epipharynx. 



SiLVESTRi on the other hand has delineated the labrum 

 on ventral view as if the longitudinal median groove were a 

 lancet-shaped organ^ (1. c p. 355. Fig. 20, B). 



Regarding the morpholgical value of the structure des- 

 cribed above it is evident from the comparison I have made, 

 that it is homologous with the organ of the Stethapathidoe 

 for which Wandolleck uses the name labrum with reserva- 

 tion, and that it does not exhibit any traces of being com- 

 posed by the coalescing of two organs. 



Furthermore I think we may safely admit that at least 

 in the Stethopathidce it can hardly be anything else than an 

 highly developed labrum. 



^ This is probably due to the dried condition of his specimen, which 

 may have caused this structure to split in several pieces. 



Arkiv för zoologi. Band 4. N:o 10. 2 



