BY R. J. TILLYARD. 



227 



times purple, and a marginal area, usually grey-black, liut sometimes purple. 

 If the divisicin between these two areas is a definite clear-eut line, it is said to 

 be eulegnic; it it is irregular and diffuse, then it is called di/slegiiic; these terms 

 being those originally proposed by Professor Poulton for similar conditions in 

 the wings of butterflies. 



Text-fig. 2. — Diagram of the markings on the forewing in the genus Eii-sthenia. hiii, 

 humeral veinlet ; /«, lunula; )\y, radial stripe ; i;«, sulihumeral oval mark. 



Text-fig. 3. — Eusilieiiia lacustris, n.sp., S ■ Anal appendages of male, lateral view 

 ( X 20). c, cercus; p, penis; sti, superior appendage. 



The males of the subfamily Eiisthciiiiiiae have a peculiar specialisation not 

 found in the Stenoperlinae. in that the penis is greatly elongated and curved up 

 over the tenth tergite. This condition is shown in Text-tig. 3. In pairing, the 

 male clings to the back of the female, but brings the tip of his abdomen round 

 under hers, so that this upcurved and dorsally coiled penis can be used to ad- 

 \antage. The penis is grooved, and the sperm ma.sses are worked by it into a 

 true spermatophore, which is held in the end-loop of the penis. How fertilisa- 

 tiim is actually effected I have not been able to see, but it would appear to be 

 done by simple transference of the spermatophore into the vagina of the female. 

 In this connection, it is interesting to note also the lack of specialisation of the 

 vulva of the female. In most Stoneflies this is a definitely projecting and often 

 strongly bifid process; but in the Eustheniinae the distal border of the ninth 

 sternite forms only a very slight undivided process. By strong muscular action, 

 the female is able to compress her end segments laterally, giving a wide gape 

 between the uintli and tenth sternites; and this evidently facilitates the process 

 of fertilisation. 



