1922] Uichanco — Notes on Parthenogenetic Macrosiphum 07 



the base of the clypeus. The insect slowly forces its way through 

 the opening thus made, in the meantime increasing the length of 

 the rent posteriorly along the dorsomedian line of the body, 

 until the caudal margin of the metanotum is reached. The 

 method of formation of the initial rupture has not been observed. 

 Neither has the mechanism of propulsion of the aphid, as it 

 glides by degrees forward, out of the exuviae, been satisfactorily 

 determined. It is, however, evident that the legs are not of 

 assistance until later in the process. In all probability, the 

 force of expansion of the insect's body itself directs the course of 

 the movement through the slit, this opening furnishing the 

 point of least resistance in the tightly fitting exuvise. The head 

 naturally goes out first, being nearest the rupture; and the 

 opening enlarges as the more bulky thorax and abdomen pass 

 out. The pro- and mesothoracic legs soon become disentangled, 

 and it is remarkable how quickly the insect is able to spread 

 them apart and use them to help force the rest of the body out. 

 Apparently, sometime before, or during the earlier part of ecdysis, 

 the chitinous coating of the appendages of the future succeeding 

 instar has a chance to harden. The concluding part of ecdysis, 

 when only the caudal portion of the abdomen and a fraction of 

 the metathoracic tibiae and their tarsi remain in the exuvise, 

 goes on as slowly as the earlier part of the process. The insect 

 never seems to be in a hurry about extricating itself, and, on the 

 whole, the molting of an aphid is an extremely sluggish operation- 

 Finally, the hind legs are set free, but, even then, the insect con- 

 tinues to remain attached with the abdominal cauda enclosed 

 within the ensheathing exuviae. The legs sway up and down and 

 the antennae remain in their posteriorly directed position. Ap- 

 parently this delay in freeing itself is an important step in the 

 molting process, as it enables the chitinous layer of the body and 

 of the appendages to get dry in the outside air and increase in 

 firmness, until it is safe enough for the insect to turn itself loose. 

 After about five minutes, or so, the fore and middle legs execute 

 a forward crawling motion and the hind legs kick against the 

 exuviae, the aphid ultimately making its escape in this manner. 

 The entire molting process, from the appearance of the initial 



