MUSCULATURE OF CULEX PUNGF.NS. 297 



Breed ('03) accounts for the wing and leg muscles of the 

 imago by a direct metamorphosis. Carrying the degeneration 

 to a few cylindrical strands of undifferentiated sarcoplasm which 

 contain many nuclei undergoing rapid amitotic division, there is a 

 period of little change followed by the appearance of the fibrillae 

 of the adult muscle. A little later the elongated nuclei which 

 have formed by the direct division disappear and short oval nuclei 

 are found scattered through the muscle substance. As for the 

 histogenesis of irnaginal muscles which are not present in the 

 larva, he gives no definite information. They are probably 

 derived from cells which resemble tracheal cells but have a dif- 

 ferent origin. 



The conditions found in Cttlc.v, as regards these points, seem 

 rather to confirm the views set forth by Korschelt and Heider 

 ('99). The destruction of the larval muscles is complete. New 

 muscles form from embryonic rudiments present in the imaginal 

 discs. A thickening of the cells at points along the under surface 

 of the hypodermis is found in the thorax, from which, after the 

 degenerative process is well advanced, cells proliferate and extend 

 into the thoracic cavity. These cells lie in irregular masses, but 

 soon form linear series as they extend inward. Mitotic figures 

 have been frequently noted among them. The protoplasm of 

 these cells is not distinct, but large oval nuclei arranged in the 

 line of their long axis appear soon to lie in a syncytium which 

 assumes the shape of a muscle fiber. This condition is repre- 

 sented in Figs. 5 and 6 of Plate XI. Already a longitudinal stri- 

 ation is somewhat apparent in the former, but this becomes more 

 marked in a later stage as shown by the latter figure. Here the 

 amount of protoplasm is increased very considerably and the 

 nuclei are pressed to the side of the fiber, and instead of being 

 the most prominent part of the structure, often show little more 

 than a granular material forming a line along the side of the fiber. 

 The greater number of these nuclei atrophy and disappear at a 

 later period, while the protoplasm continues to increase. An 

 advanced stage which occurs late in pupal life and marks the 

 completion of the morphological characteristics of these muscles 

 by the appearance of transverse striae is represented in Fig. 4, 

 Plate XI. The nuclei have all disappeared except those which 



