BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 351 
The course of events in the destructive changes of the contractile 
substance is quite evident from these three stages. The muscle columns 
break up into their primitive fibrillae, and these then undergo dissolution. 
The sarcoplasm increases in amount during this process, but not enough 
to balance the loss in volume caused by the dissolution of the fibrillae, so 
that each fibre shrinks in actual volume. This is shown by a determi- 
nation of the volume of the largest fibre of musculus metanoti (Plate 1, Fig- 
ure 1, mé’nt.) in each of the three stages described. Of course there is a 
chance for error in this determination, in that the muscle fibres vary in size 
in different individuals; but the ratios of the volumes in the three stages 
will at least give an indication of the amount of shrinkage. The ratios 
. . stage 1:11: 1 
of the volumes are in the case determined very nearly, Tosa EA 
From this it seems probable that not all of the material derived from the 
dissolution of the fibrillae is transformed immediately into sarcoplasm, 
but that some of it remains for a time in solution. It is suggested above 
that the agent which causes this dissolution is the sarcoplasm. There is 
no evidence of the action of leucocytes, either phagocytic or lyocytic, 
since they come into the neighborhood of the muscles only occasionally ; 
nor is there reason for supposing action on the part of other outside 
agents. 
During. the whole period of these destructive changes the muscle 
nuclei undergo frequent amitotic divisions. The larval nuclei (Plate 7, 
Figure 34, nl.) before division are comparatively large, with usually a 
single definite nucleolus. Figure 34 shows a nucleus dividing amitoti- 
cally (nl.*) and three pairs of smaller nuclei (n/.”), the resultants of 
such divisions. At pupation very few of the nuclei presenting the 
characteristics of ml. are found, whereas very much elongated nuclei 
(Plate 6, Figure 25, ni.,? shows one that is comparatively short) are found 
associated with strings of nuclei which have arisen from the division of 
such elongated ones. Many of these nuclei no longer lie at the periphery 
of a fibre, nor even at the periphery of one of the strands which have 
arisen from the division of a fibre, but are deeply embedded in the 
muscle substance (Figures 14, 27, 28). 
The sarcoplasm found at the surface of the larval fibres becomes lost 
at an early stage, intermingling with the increasing amount of sarcoplasm 
between the fibrillae. 
The only tissues, other than the muscular, which need to be considered 
in this connection are the tracheae and the embryonic tracheal cells. 
The tracheal endings on the muscles before any change takes place have 
