bkeed: metamoephosis of the muscles of a beetle. 361 



from the structureless muscle substance containing the larval nuclei is 

 the same as the reconstruction of the leg muscles. That is, longitudinal 

 fibrillation appears first, then cross striation, the latter appearing about 

 the time of the emergence of the imago. At the same time Cohnheim's 

 areas become plainly distinguishable, and have the pattern shown in 

 Figure 20 (Plate 6), which is drawn from the cross section of a single 

 fibre of the foreintestine of the imago. The muscle substance, when 

 structureless, stains deeply with thionin, but after the fibrillae are 

 formed, it stains scarcely at all. The nuclei remain as they were, while 

 a new sarcolemma is formed about each fibre in the old pupa. The 

 tracheal cells of this region give rise to the new tracheae and possibly, 

 as stated before, to imaginal leucocytes. 



Deegener, who speaks of these tracheal cells as spindle cells (page 146, . 

 et seq.), derives the intestinal musculature of the imago from them. He 

 gives no conclusive proof of this derivation in any case, however. In 

 the region of the midintestine he was unable to distinguish these 

 spindle cells with certainty, so that his conclusion that the muscles of 

 this region are formed from these cells is pure assumption. He is 

 forced to make such an assumption by his conclusion, — which has 

 already been shown to be incorrect, — that there is a phagocytosis and 

 total destruction of the larval muscles. Thei'e is no reason for suppos- 

 ing that these cells form the intestinal muscles of the imago any more 

 than that they form the muscles of the remainder of the body, and this, 

 as has been shown, is not true. 



c. Histolysis of the Larval Muscles. 



The muscles which undergo histolysis in the pupa present great indi- 

 vidual variation as to the time when degeneration begins. There are 

 also variations in the details of the degeneration, which are of such a 

 nature that they form a partial transition to metamorphosing muscles. 

 However, no instance of a muscle which sometimes degenerates and 

 sometimes metamorphoses into a rudimentary imaginal muscle has been 

 found, though it does not seem improbable that such may be present 

 in some of the beetles. 



The group of muscles of the metathorax designated in Figure 1 (Plate 

 1) by the Greek letters /3, y, 8, e, ^ rj belong to a class of degenerating 

 muscles which are very distinct from the metamorphosing muscles. This 

 group will servo as a type in describing the degeneration and the differ- 

 ences between these and the other degenerating muscles noted later. 

 The substance of these degenerating muscles never stains with thionin. 



