THOMPSON: ANATOMY OF MOSQUITO. 
199 
maxillary palpi, thoracic limbs, wings, halteres, and gonapophyses 
are developed as invaginate buds. But the invaginations are very 
shallow in most cases and in the deepest of them — those for the 
antennae — the connection with the surface of the head is a wide 
channel. During the pupal stage the hypodermis of the mid-dorsal 
face of the labium thickens and forms a low ridge, beneath which 
cells build the salivary gutter. In male pupae the ridge disappears 
as soon as the salivary gutter is formed. In female pupae it sepa¬ 
rates from the labium and becomes the hypopharynx. 
The longitudinal and circular muscles of the walls of the alimen¬ 
tary canal and most of the head muscles are completely histolyzed. 
It seems likely, however, that the head muscles and the muscles of 
the walls of the gut in the perfect insect are derived from myoblasts 
which are descendants of nuclei of the older muscles. A few of 
the muscles in the head undergo a partial degeneration only and 
in a sense give rise directly to imaginal bands. The muscles of the 
wings and legs of the imago are new with the pupa stage. The 
rudiments of the former series appear during the last part of the 
larval period. 
The epithelium of the midgut, i. e ., of cardia, caeca, and stomach, 
is sloughed and is replaced by a new epithelium derived from 
scattered regenerative cells. These appear during the larval stage, 
multiply rapidly, and during the early part of the pupal stage form 
an epithelium which displaces the older cells. The latter fall into 
the lumen and are absorbed. The larval colon is completely histo¬ 
lyzed and a canal which grows into its lumen by proliferation of 
cells of both ileum and rectum replaces it. Prior to this growth, the 
epithelium of the ileum undergoes a partial degeneration. Hence 
the posterior end of the imaginal ileo-colon is a new structure. 
The anterior end consists mainlv of remodeled cells of the older 
epithelium. In the rectum the anterior portion has a metamorpho¬ 
sis similar to that of the ileum. The posterior end is rebuilt from 
an anal ring of regenerative cells the origin of which is uncertain. 
The metamorphosis of the alimentary canal of Culex presents par¬ 
allels to the postembryonic development of the most specialized flies. 
Thus, a belt of differentiated cells forms near the cardiac end of the 
fore gut, recalling in its position the anterior imaginal ring of Musca, 
from which much of the foregut of the imago is derived. In Culex 
the ring is remodeled to form the esophageal valve. The anal ring 
