152 THP: CANADIAN ENTOMOLOGIST. 



seemingly, as he counts the "segment mediaire," of which he says, p. 630, 

 "its sternum appears to be undeveloped." He calls the antennae pale- 

 tipped. Perhaps this belongs, as in the male, to the apical joints, which 

 are wanting in my specimen. 



It is doubtless true that the specimen just described is a female, as 

 Mr. Wood-Mason has well proven by the location of the genital aperture 

 between the 7th and 8th ventral segments ; also that it is a full-grown 

 female, as proven by the firmly chitinized integuments. How Mr. Wood- 

 Mason arrived at the previous conclusion, that the females of Embia 

 would be apterous, I do not know ; though his supposition that the female 

 would be probably larger in size, was justified by related families. In 

 accepting solely on the high authority of Mr. Wood-Mason and Mr. Mc- 

 Lachlan that this female belongs to O. Michae/i, it seems important to 

 point out the differences of the male (after the description and figure by 

 McLachlan) and the female. 



1. The difference in size is very great, body of the female being at 

 least one third longer, and half broader. 



2. The female is perfectly wingless ; no traces of rudimentary wings to 

 be found at the anterior angles of the two thoracic segments. There 

 seems to be indeed at the anterior angles a little below the dorsal plate, a 

 very small hyaline membranous sac, but the insufiicient material at hand 

 would not justify the accepting of these sacs as traces of aborted wings. 



3. The difference between the eyes of the male and the female is very 

 striking, though not noticed by the author. The male has large eyes, pro- 

 minent on the sides of the head, very visible from above, kidney shaped, 

 and the socket of the antennas placed in the emargination ; the facets are 

 globular. The female has the eyes much smaller, scarcely visible from 

 above, below and behind the antennae, from which they are wider separ- 

 ated ; the hind part of the eye is about half broader than the front part ; 

 no inner emargination exists ; the facets are smaller and flattened. The 

 eyes of the male are more like aggregated eyes (Stylops), the eyes of the 

 female are like the common compounded eyes of insects. The conse- 

 quences of these differences are very visible in the shape of the head. The 

 largest diameter of the head of the males is situated between the eyes ; 

 behind them the sides of the head slope down to the occiput. The head 

 of the female is nearly orbicular, or at least very shortly ovoid. A sexual 

 difference of the eyes does not exist, as far as known to me, among the 

 Perlids, but very often in Psocids and Ephemerids, 



