108 THE entomologist's record. 



The tube forming the "vesica" must penetrate all the way, and 

 not only so, but must do so as a double tube, i.e., the tube as it enters 

 must gradually be everted, precisely as the whip-like tails of Centra 

 larvfe are everted, only the process is not completed as in the puss- 

 moth larva, but there is still within the outer portion of the tube when 

 the process is complete, a part of the inner portion. The ^ tube 

 engaged must therefore be of practically twice the length of the $ tube. 

 In this way there is no gliding of the wall of the c? tube along that 

 of the 2 , each portion of the 3 tube as everted will remain at the 

 point of the 2 tube where it is everted, the process being continued by 

 the inner portion of the J tube pushing forward to be everted in its 

 turn. This process would go on until the portion of the tube carrying 

 the cornuti becomes everted in the sac or sacs of the bursa. In this 

 way the cornuti do not, as one is inclined at first to think must 

 be necessary, pass up the ? tube as an advance guard, themselves in 

 contact with the ? tube and rubbing along it, and presenting terrible 

 difficulties of the sharp points catching in or even piercing its walls. 

 Between them and the J tube are the double walls, the direct and the 

 inverted, of the 3 tube (or " vesica "), and the only parts that slide 

 over each other are the opposed visceral surfaces of the ^ tube, those of 

 the part already everted that is at rest as a lining to the portions of ? 

 tube already penetrated, and of the portion that is still advancing 

 within the portion at rest. 



When the male tube is withdrawn the corunti present no greater 

 difficulty theoretically to be withdrawn with it, than they did to 

 their entrance, and as a matter of fact, in many insects there are very 

 elaborate and complicated spines arising from the vesica, that are so 

 withdrawn after having served their purpose, whatever it is. 



In our Fyraiista aitrata, however, it has obviously been of some 

 advantage not to withdraw the cornuti with the tube, but to leave them 

 behind. Possibly where the tubes are so lengthy and convoluted, as 

 in this species, the withdrawal is easier without them and can conse- 

 quently take place more rapidly, and may thus present some advantage 

 under circumstances of danger when each insect may more readily 

 escape, if rapidly liberated, to seek safety. 



I may rem^ark that my idea of how these cornuti are introduced is 

 purely theoretical, deduced from examining the structures. It seems, 

 however, to be at variance with the fact that the position of the 

 cornuti within the fedo?agus suggests that they lead the way and 

 advance in front unsheathed. The question seems to me one that 

 may perhaps be solved by further observation, which will, however, be 

 very difficult. The real support of my theory is that one does often 

 see the vesical tube extended by this process of eversion, and that 

 unquestionably wherever it extends to in the female passages it does 

 so as a double tube. It is also in full agreement with the scheme of 

 these parts that is expressed by Dr. Sharp, Trans. Knt. Soc. Ijmd., 

 1912, p. 600, in the statement that the S tube forms " a perfect tube 

 without orifices." He describes the apparent orifice as due to " the 

 invagination of the tube into itself." The process of penetration, 

 which I have attempted to describe above, might be more simply 

 defined as the evagination of the tube. 



