I 



415 



considerable area of the apex of the head (fig. 154), all upon 

 the narrow cell column. During the first day of pupal life 

 ectodermal cells still more distant — on a great part of the 

 posterior, and also lateral, regions of the head — elongating 

 considerably, insert their processes upon the secondary cell 

 columns. These processes then apparently contract again, 

 and the tension exerted by these appears to overcome that 

 which holds the secondary columns together ; they break apart, 

 and, the ectodermal insertions contracting more and more, 

 idrag these columns into the positions they are to occupy in 

 bhe adult insect (fig. 114). 



At their lower extremities the spreading out of the cell 

 columns is much more limited; they do not encroach upon 

 large areas of the ventral portion of the head, but confine 

 themselves to the mouth appendages, which have meanwhile 

 developed, and in close contact with which they have always 

 been. 



Even in the pupa in its third day the cell columns may 

 still be observed in this condition. The ectodermal insertions 

 have retracted, and evidently exert a considerable tension on 

 the columns. These are seen to consist of about eighty cells, 

 arranged one behind the other; only the outer cell walls have 

 persisted, so that they now form each a syncytial column, 

 already visible as such in the thirty-six hour pupa. Each 

 nucleus has a distinct karyosome, lying within the slightly 

 granular nuclear space. 



During the fourth day of pupal life the muscles begin to 

 show striations — again of the spiral type — and the muscle 

 passes into its adult condition (fig. 116). The persisting cell 

 walls remain as the sarcolemma. 



The labium is provided with a set of powerful muscles 

 which have probably been formed from the great cell columns ; 

 during early pupal life they become inserted on the posterior 

 wall of the head, just above the labium. 



In the proximal joints of the antennae, myoblast cells, 

 which in the early larva were dragged into the antennae as 

 these grew outwards, form, in the defaecating larva, a cell 

 column in the basal joint of each antenna. These cell columns, 

 growing backwards, meet the lower portions of the integu- 

 mental ingrowths which produce the great cephalic phragmas 

 already referred to, and spreading out in a number of separate 

 columns on these (fig. 43), produce, by a process similar to 

 that above described, the muscles of the antennae. It should 

 be noted that only the first joint of the antennae is provided 

 with muscles. The cephalic phragmas are strengthened by 

 the attachment to their posterior surface, of certain of the 

 muscles of the mouth appendages. 



