21'. 



PSYCHE. 



June, lyoi 



along the median line of the back. [To 

 see this well cut out the median dorsal 

 strip of body wall carrying the heart 

 and transfer it to a glass slide. Cover 

 with water and examine first under the 

 simple microscope and then under the 

 low objective of the compound micro- 

 scope.] It will be distinctly seen that 

 toward the middle of each segment, 

 from the last to the third inclusive, the 

 tube becomes dilated and in most of 

 these swellings except the last a pair of 

 internal valves may be seen. From the 

 anterior of these a straight anteriorly 

 tapering tube, the aorta, extends for- 

 ward into the head where it ends in 

 branches. [Make a drawing of the 

 heart and aorta.] 



Attached to each dilatation of the 

 heart are two fan-shaped gioups, one on 

 each side, of very delicate muscle 

 fibers, called wing muscles from their 

 shape. The convergent outer ends are 

 attached to the body wall on the line of 

 the median constriction in each seg- 

 ment. These muscles are easily seen 

 under the compound microscope. 



The iinaglnal buds of wings and legs. 

 [ Returning to the first specimen (that 

 opened along the dorsum) carefully 

 remove the muscle fibres from the body 

 wall of the three front (thoracic) seg- 

 ments of the body, not including the 

 head. Be careful not to pick away cer- 

 tain small whitish bud-like bodies lying 

 between the muscles and the body wall.] 

 In specimens of sufficient age the iniag- 

 inal buds of the wings and legs and of 

 the external prothoracic respiratory 



tubes of the pupa may be seen as small 

 sac or bud-like bodies lying against and 

 attached to the inner surface of the 

 body wall of the thoracic segments. 

 There are two pairs of these imaginal 

 buds in each thoracic segment corres- 

 ponding respectively to the prothoracic 

 legs of the imago and prothoracic re- 

 spiratory tubes of the pupa, the meso- 

 thoracic legs and wings of imago, and 

 the metathoracic legs and halteres of 

 the imago. The morphology and devel- 

 opment of these imaginal buds will be 

 the subject of the next paper in this 

 series. 



Tlie head sckrites and mouthparts . 

 [After finishing the dissection of the 

 internal organs remove the head entirely 

 from the rest of the specimen and ex- 

 amine under the simple microscope]. 

 Each of the short antennae arises from 

 a small lobe on the plate covering 

 the top of the head. This plate is 

 long, tapering and decurved be- 

 hind. Anteriorly along its sides it is 

 united with the lateral plates, while the 

 anterior margin is reentrant receiving 

 the smaller end of the pear shaped 

 labrum (upper lip). The distal part of 

 this sclerite is membranous except for 

 two lateral chitinizations. Posteriorly 

 it is fused with the epicranial plate. The 

 lateral plates are each oval, shell-shaped, 

 having their anterior lower angles pro- 

 duced forward and united with each 

 other. The single process thus formed 

 projects forward and curves upward be- 

 tween the faces of the posterior jaws. 

 The tips are provided with graduated 



