j6 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vol. 50 



fully formed hook no living substance (marrow of hypodermal 

 matrix) is present. A regeneration of worn off hooks is therefore 

 impossible. The cuticule of the upper wing-lamella, pierced by the 

 hooks, sinks clown around their basal ends, round which it is thick- 

 ened and from which it is divided by an incision. (The depression 

 is shown in fig. !>?>, the incision in fig. 32 on plate x.) On the 

 whole the hooks are developed in the same manner as the hairs and 

 scales of the Lepidoptera, the development of which has been de- 

 scribed by Semper (1857, pp. 326-339). Like these unicellular struc- 

 tures which are fully chitinized in the developed animal, they are 

 neither capable of secondary growth nor of regeneration. 



The groove-like plicature of the posterior margin of the fore wing 

 is formed rather late, about the time when the coloring of the body 

 commences. The upper wing-lamella takes a more prominent part 

 in the formation of the groove than the lower. This predominance 

 of the upper over the lower lamella, clearly recognizable also in other 

 respects, is particularly noticeable during development (pi. x, figs. 

 34,35)- 



V. Function of the Clasping Apparatus 



The connection established between the fore and hind wings by 

 means of the hooks and groove is extremely close and energetically 

 maintained. It is only with difficulty that the hind wings can be 

 detached from the fore wings in the living animal without injuring 

 the wings, and as soon as one lets go, the parted wings are imme- 

 diately reunited by a powerful stroke. What functions pertain to 

 the different parts of the clasping apparatus during flight and in 

 what manner they are brought into play may be elucidated by a con- 

 sideration of the wing-stroke. The position of the wings is, accord- 

 ing to Marey (1869, p. 667), such that in the downward stroke the 

 upper side of the wing faces obliquely forward ; in the upward stroke, 

 obliquely backward. At the same time the apex of the wing de- 

 scribes a line approaching the shape of the figure 8, with narrow 

 upper loop (1872, p. 2). 



The accompanying diagram shows approximately the position and 

 direction of the two wings in the principal phases of a wing-stroke. 

 It can be seen that, in the upward as well as in the downward stroke, 

 the fore wing drags the hind wing after it, the latter as it were hold- 

 ing on to the groove of the former by means of the distal hooks. As 

 the connection of the wings is not rigid, the hind wing forms an 

 obtuse angle with the fore wing. Firmly clasping, stout, and 

 strongly bent distal hooks and a deep and firm groove will be 



