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 Cyllene 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 ‘‘ Kérnchenkugeln,” or similar bodies, but 
none have been seen in these forms. 
