C)8 PSYCHE [October 



the beak and extend to the tip giving off branches en route. A cross section of 

 these tracheae as they appear in the pupa (fig. 16 /r.) is remarkably like a section 

 of tendon or of salivary gland ; but in the adult (fig. 17 /•/-.) they are seen to be Lined 

 with chitin — not filled with it, as are the tendons. 



The further development of the beak consists in the thickening and proper 

 shaping of its cliitinous walls, the appearance of scales developed from mother-cells 

 early differentiated in the hypodermis, the shaping and perfecting of the armature 

 and articulations of the mouth parts, the elongating of the pharyngeal processes of 

 the mandibles and the development of the prickles upon their surfaces, and the 

 differentiation between dorsal and ventral walls of the pharynx in which they lie, 

 as already described under the account of the adult, and as sliown in fig. 17, the 

 developing of the semicircular muscles on the dorsal side of the pharyngeal wall, and 

 the circular muscles about the esophageal wall, and the two rows of elevator muscles 

 attaching to the chitin of the dorsum of the beak in both regions. 



The Develop.ment of the Antennae. 



The antennae of Rhyncophora show considerable differentiation of segments, 

 being geniculate at base and clubbed at apex — a condition that is attained by them 

 in early pupal life as shown in Plate VIII, fig. 11. At this stage the composite 

 nature of the club is apparent and the segments of the pedicel lack much of their 

 definitive length and slenderness and complexity of structure. In the pupa when 

 first formed (fig. 10) these parts are hardly differentiated : the scape is exceed- 

 ingly short, and segmentation is incompletely indicated, even in the pedicel. But 

 the younger specimens (larvae) already referred to (Plate VI, figs. 3-5) show already 

 indications of a terminal club and a geniculate base. It is doubtful whether all 

 the transverse constrictions and convolutions that appear at this time really repre- 

 sent the segments that will appear later, for these are probably due in a large part 

 to growth witiiin the narrow confines of the loosened head capsule. 



To find the beginnings of the antenna one must study sections of the head of 

 the full grown larva before metamorphosis has begun, and before the chitinous head 

 capsule has been loosened. Then one may find in the position of the base of the 

 larval antennae in other coleopterous larvae the antennal buds — mere disks of 

 thickened hypodermis, not invaginate nor in any way removed from the surface, 

 surrounded by a circular groove and a circular ridge of hypodermis (the equivalent 

 of the peripodal membrane of " imaginal discs ") as shown in Plate VII, fig. 6. The 

 shallow internal cavity is filled with fat cells and leucocytes. Already there appears 

 a thin layer of neuroblast (?) cells, attached to the inner ends of the hypodermis 



