SCENT ORGANS IN TRICHOPTERA. 463 
laterally (text-fig. 2). Together they entirely cover up the front 
of the head or clypeal region. Their tips are received each into a 
slot or excavation of the inner side of the enormously enlarged 
basal joints of the antenne (text-figs. 4 & 5); emerging from 
underneath the palpi may be observed the tip of the white fleshy 
haustellum, the white tip of the labium and the lobes of the first 
maxille. 
Text-figure 2. 
Sericostoma personatum, 6. 
Head, side view (diagrammatic). 22. 
E. Eye. Aj. First segment of the antenna. F. Genal flap. C. Cardo. 
ST. Stipes. H. Haustellum. JP. Palpus of the first maxilla. LP. 
Palpus of the second maxilla. SW. Subocular wart. 
In order to understand the modifications which have been 
drawn in the train of the enormous enlargement and porrec- 
tion of the maxillary palpi, a few words are necessary upon 
the maxillary palpi and the structure of the head in other 
Trichoptera. In this Order, with the exception of Plectrotarsus, 
Chimarrha, and Ptilocolepus*, the lower side of the skull is 
incomplete, the gular region from the occipital foramen to the 
labiam being soft and membranous. On either side the two 
* The species examined were Plectrotarsus gravenhorstii Kolenati, Chimarrha 
argentinea Ulmer, and Ptiloculepus granulatus Pictet. P. gravenhorstii is the 
only species known belonging to its genus, and in the other genera it has been 
assumed that the observations following, recorded for the particular species, apply 
as well to the rest of the species of the geuus. 
