30 Psyche [April-June 



ently decisive test for determining whether an insect is lepidopter- 

 ous or trichopterous, and when this test is appHed to the microp- 

 terygoids, they are seen to be clearly lepidopterous, not trichop- 

 terous! The "transversely ovate" outline of the mesothoracic 

 scutellum (Fig. 8, "SI2") in most Lepidoptera as opposed to the 

 triangular scutellum of most Trichoptera (Fig. 5, "SI2"), the 

 absence of a median ocellus in all known Lepidoptera and its 

 presence in some Trichoptera, the presence of "scales" on the 

 maxillary palpi of some Trichoptera and their absence in all known 

 cases in Lepidoptera, and the presence of structures homologous 

 with the posterior abdominal styli in all trichopterous larvae ex- 

 amined, coupled with the absence of such structures in lepidop- 

 terous larvae are features of value serving to support the above 

 mentioned test, when applied to the micropterygoids, and the 

 evidence furnished by these features (which seem to have a very 

 general application throughout the two orders) should be conclu- 

 sive. I would therefore maintain that the micropterygoids are 

 lepidopterous, not trichopterous, although I too would emphasize 

 the remarkably close relationship between the lower Lepidoptera 

 and Trichoptera (See Trans. Ent. Soc. London, 1919, p. 93). 



In the appended diagram (text figure 1) the lines of descent of 

 the Lepidoptera and Trichoptera are represented as though diverg- 

 ing from a common Lepidoptero-Trichopteron stem composed of 

 forms combining in themselves the primitive ancestral features of 

 the two orders. Just after these two lines of descent begin to 

 diverge as they emerge as distinct orders (the common stem, 

 however, was probably trichopterous) the line of development of 

 the micropterygoids appeared, carrying over from the common 

 ancestry many primitive features occurring in the Trichoptera, 

 yet exhibiting certain peculiarly lepidopterous characters. The 

 line of development of such Trichoptera as Philopotamus likewise 

 arose very near the point of origin of the micropterygoid line of 

 development, as shown in the diagram, but since Philopotamus' 

 line of development is on the side of the Trichoptera, it did not 

 acquire any peculiarly lepidopterous features, though it has 

 developed certain features in common with all other Trichoptera, 

 as would naturally be expected. This simple and self-evident 

 explanation will serve to show how the micropterygoids may be 

 truly Lepidoptera, and the Philopoiamus-Yike forms may be truly 



