FORMATION OF ANTENNA 



657 



ages being only the point of departure of the imaginal growth. 



Weismann has observed in Corethra how at the approach of each 



moult an invagination like the finger of a glove allows the antenna 



to elongate from its base. The process, says Gonin, is identical in 



the caterpillar of Pieris. At the last 



moult the invagination is so pronounced 



that it is not effaced with the renewal 



of the chitinous integument. Several 



days latej.- it again begins to grow larger. 



As the imaginal bud gradually sinks 



into the cavity of the head, it presses 



back the hypodermic wall and thus 



forms an envelope around it. Its base, 



widely opened, gives admission to the 



nerves, besides capillaries and sometimes 



a large trachea. 



As soon as it reaches the posterior 

 region of the head, the antenna in 

 lengthening becomes folded and describes the great curves which 

 led Reaumur to compare it to a rain's horn (Fig. 613). The leaf of 

 the envelope thickens in the interior and all around the base of the 

 organ. Its ultimate role is closely like that of the two other hypo- 

 dermic formations. It is at the outset this layer of cells which in 



FIG. 610. Larva in same stage as 

 Fig. 613 ; side view uf head and thorax : 

 a, a', wings, with the folds on the sur- 

 face, and the sinuous track of the 

 tracheal bundles ; st /, prothoracic 

 stigma; p, p', ends of the legs. 



..jn 



FIG. 611. Head of the larva just 

 before pupation : between the two man- 

 dibles (m) is seen the relief of the tongue 

 or maxillae (m');f, spinneret; I, labrum ; 

 a, antenna. 



t 



FIG. 612. Same stage as in Fig. 611, but after the 

 removal of the larval skin, and including the lateral scale : 

 A, side, B, front, view; c, "cimier" (the dotted line 

 shows the position it takes in the pupa) ; a, antenna ; 

 o, eye ; t, tongue. This and Figs. 603-611, after Gonin. 



the larva supports the ocelli. This layer, hidden on each side under 

 the parietal region, thickens and regenerates, forming a circular pad 

 which becomes more prominent and finally assumes the form of the 

 compound eye of the imago. 



Finally, this layer gives rise to a conical prolongation (Fig. 612, c), 

 which after exuviation appears as a tuft of long hairs, and is called 

 2u 



