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TEXT-BOOK OF ENTOMOLOGY 



connection just mentioned as the long drawn-out neck of this 

 invagination. 



In general, the development of the appendages (Figs. 626, 627) 

 goes on as described in Corethra. The rudiments of the legs enlarge 

 and show at an early date the first traces of the later joints. They 

 are so packed in the peripodal cavities that the single joints of 

 the extremities appear as if pushed in " like the joints of a travelling 

 cup." (Van Eees.) The evagination of the completely formed buds 

 of the limbs, which occurs on the first day after the beginning of 

 pupation, goes on in such a way that the stalk of the imaginal bud 

 (Figs. 626, B; 627, B) shortens, while its cavity widens so that the 



FIG. 627. Imaginal buds of inuscid Hies in process of development: A, brain (c) and ventral 

 ganglion (r) of a larva. 7 nun. Knur, of '\ romitoriii : h, heart-rudiment ; re, portion of ventral cord ; 

 pd, prothoracic rudiment ; rc 3 , third nerve ; md . mesothoracic rudiment. B, mesothoracic rudi- 

 ment more advanced, in a pupa, just formed, of Sa /'<;>// ga carnurin, showing the base of the 

 sternum and folds of the forming leg. the central part i / ) representing the toot. (.'. the rudimentary 

 leg of the same more advanced ; /, femur ; t, tibia ; J\, /j, tarsal joints. /), two buds from a larva, 

 20 mm. long, of Sarcophaga. attached to trachea- : //<*. im-sc>notal and wing-germ : inf. metathoracic 

 rudiment. E, r, mesothoracic germ of a 7 mm. long larva attached to a tracheal twig. After 

 Weisinann and Graber, from Sharp. 



limbs finally, as in Corethra, pass out through the widely opened 

 mouth of the peripodal invagination, which at the same time gradu- 

 ally completely disappears. The peripodal membrane is converted 

 into a thickened part of the hypoderrnis in the region adjoining the 

 base of the leg, and from this thickened hypodermal portion, the 

 formation of the hypodermis of the entire imaginal thorax goes on, 

 as the larval hypodermis is gradually destroyed. 



We must here settle the question as to the first origin of the mesoderm.il 

 portions of the rudiments of the appendages. We can already distinguish in 

 the imaginal buds of the fully grown inuscid larva a clear separation between 

 an ectodermal and an inner uiesodermal part. Ganin derived the mesodermal 



