BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 365 



impossible to distinguish them from the mesoderm cells. But from 

 analogy with the remainder of the body, it is very likely that they have 

 not persisted from embryonic life, but are developed during the period 

 of the resting larva from the tracheae which supply the masses of tissue 

 at the bases of the legs. They develop into the tracheae of the legs of 

 the imago. 



In young pupae in which the legs have grown to some size, in the 

 places where new muscles are to be formed, there may be found groups 

 of cells already transforming into muscle fibres. Between these form- 

 ing fibres are to be seen free cells, many of which are dividing mitotically. 

 These may now be recognized as tracheal cells, which are precisely like 

 the cells found associated with the metamorphosing muscles of the 

 remainder of the body. The muscle nuclei in the earliest stages in which 

 they can be recognized as such are seen to be undergoing frequent 

 amitotic divisions. From this time on the amitotic is their only 

 method of division : a thing which is characteristic of the nuclei of all of 

 the muscles which have been studied. The muscle fibres increase rapidly 

 in size, and it very soon becomes impossible to distinguish them from the 

 metamorphosing muscles of the leg type, which meanwhile have com- 

 pleted their destructive changes, and are starting on their reconstruction. 

 The tracheal cells remain as free cells between these fibres until a late 

 stage of the pupa, when they form tracheae in a manner similar to that 

 already described for Thymalus. 



The question whether each muscle fibre is developed from a single 

 cell or not, is almost impossible to settle in this case. There cannot be 

 much fusion, however, as the fibres of the completed muscles are almost, 

 if not quite, as numerous as the cells from which they are developed. 



The metamorphosing, degenerating, and persistent larval muscles of 

 Bruchus obtectus show conditions exactly comparable with those of Thy- 

 malus. The fibrillae of the indirect wing muscles are larger in Bruchus, 

 and their development in the structureless sarcoplasm of these muscles in 

 the pupa is much more obvious than in Thymalus. No leucocytes with 

 inclusions have been found at any stage, though a careful search has been 

 made for them. 



Sections of larvae and pupae of Synchroa punctata Newm., a Melan- 

 dryid oak-bark borer, and Cylleue pictus Drury, the common Cerambycid 

 hickory borer, have also been examined. The muscular changes of 

 these forms are essentially like those already described. A sharp look- 

 out has been maintained for " Kornchenkugeln," or similar bodies, hut 

 none have been seen in these forms. 



