SCENT ORGANS IN TRICHOPTERA. 461 
retractile tubular filaments have not yet been described from 
the Trichoptera. 
Under the term “scent glands” it is necessary also to include 
those hypothetical organs the emanation from which, in the females 
of certain moths, is supposed, in the well-known phenomenon of 
“assembling,” to attract males from long distances. These alluring 
glands have not, I believe, been actually located, nor has the 
nature of such emanation been ascertained. Of course odoriferous 
glands undoubtedly do exist in many female Lepidoptera, and 
recently Ernst Urbahn (21) has made a detailed study of these 
glands, which are restricted to the abdomen and occur as 
intersegmental sacs, folds, and so on. 
Then, again, in insects like the Musk Beetle (Aromia mos- 
chata), scent glands of still another type are found. These are 
pluricellular and open to the exterior by an aperture. In Aroma 
they are present in both sexes, though the aroma is stronger in 
the female, while the male is the more active organism. 
It is often difficult to distinguish scent glands of this type from 
stink or repugnatorial glands used in self-defence. The resem- 
blance is increased by the fact that some organs which have been 
described as stink glands, e.g., in the Cockroach, Phyllodromia 
germanica (16), are nevertheless limited to the male. On the 
other hand, sac-like glands at the end of the abdomen of a 
Cricket, Ceuthophilus maculatus [(10) p. 393], occurring only in 
the male, are regarded as scent glands *. 
There is, indeed, a widespread confusion in the literature of 
the subject, and it is difficult or impossible, in the present state 
of our knowledge of the natural history and mating habits of 
these insects, to say whether glands, occurring as they may in 
one sex only or in both, are of sexual import or are used in self- 
defence. A priori, stink glands if used in self-defence, one would 
expect to be either common to both sexes or, if limited to one sex, 
to occur in the female rather than the male 7. 
The occurrence of typical unicellular scent glands at the bases 
of hairs in Trichoptera as well as in Lepidoptera is interest- 
ing, and in view of the close relationship of these two Orders, 
not wholly unexpected. But in consequence of the common 
occurrence of scent glands in other insects besides Lepidoptera 
and Trichoptera, this cannot be taken in itself as evidence of 
phylogenetic affinity any more than can the presence of scales, 
which are also present in Trichoptera and Lepidoptera, but 
which occur also in Thysanura and other insects. Further, 
in Sericostoma, as will presently be shown, they occur on the 
* The organs, called by their discoverer, Kraus, “ duft organe” in Aphlebia 
bivittata, ave named by Berlese “ ghiandole repugnatorie.” 
+ The stink gland, of course, must have been independently acquired very many 
times, for it is a device for self-defence adopted by many animals in very different 
phyla of the Animal Kingdom (e.g. Myriapods and Mammals). Scent or alluring 
glands are also common ‘The mammalian anal, preputial, and inguinal glands 
are doubtless of sexual importance on account of their odoriferous secretions. 
Odoriferous glands occur also in crocodiles and snakes. 
