



MUSCULATURE OF CULEX PUNGENS. 2X7 



there is no resting stage. Does the cessation of physiological 

 activity mark the beginning of degeneration here ? It cannot be 

 otherwise ; the muscles which first disappear are those of the head 

 and thorax which would be of as little use to the pupa as though 

 there were a true resting stage ; the other muscles are not lost 

 until late. Any muscle must certainly have ended its physiolog- 

 ical function before it is removed by what can be considered a 

 normal process. 



Further generalizations will be deferred until the conditions 

 observed in Culex have been described. The muscles of the 

 larva, before degeneration has begun, show the usual character- 

 istics of muscular tissue in other insects. Bundles of coarsely 

 striated fibers, each with its sarcolemma and nuclei, are arranged 

 longitudinally along the segments of the body. The nuclei are 

 oval and lie close to the contractile substance within the sarco- 

 lemma. Immediately surrounding it is a small amount of finely 

 granular protoplasm. With the onset of regressive change in 

 these muscles, there is an increase in the amount of the granular 

 material about the nucleus and the latter becomes separated from 

 the contractile substance, loses its oval shape and hypertrophies. 

 This takes place before there is any appreciable change in the 

 contractile substance. Later the striations are less distinct and 

 become gradually lost, while at the same time the fibers become 

 divided longitudinally into fibrillae. The sheath of the bundle is 

 stripped away from the fibers by an increasing amount of gran- 

 ular material, in which the hypertrophied nuclei come to lie. All 

 this takes place without the appearance from other sources, or 

 formation from preexisting elements in the muscles, of active 

 cells of any kind. 



From this stage of regression several phases of degeneration 

 present themselves, none of which are constant, nor confined to 

 any one set of muscles. The nuclei lying free in a mass of gran- 

 ular material continue to hypertrophy. The chromatin threads 

 are early lost, and small deep-staining granules appear in the 

 nuclear substance which later become arranged about the peri- 

 phery close to the membrane. The nucleolus disappears at this 

 time, and the center of the nucleus may be almost transparent. 

 Finally the membrane ruptures and the granules become scattered 



