366 THE AMERICAN NATURALIST. (Vou. XXXV. 
and the muscles of the head than in any complete substitu- 
tion of an imaginal musculation for a previous wholly different 
complex larval musculation. In pupa one-third through their 
existence (four days old) a great deal of the larval muscula- 
tion still persists side by side with the developing new muscles 
of the thorax. The nuclei of the degenerating larval muscles 
show the “old-age” characters of degenerating nuclei; the 
contractile substance first loses its striate appearance, then 
becomes loosely fibrous, then spongy, and finally breaks up. 
The degeneration of the large salivary glands is easily fol- 
lowed. In the larve the nuclei of the large epithelial cells 
@ 
pup y-eig ld, degenerati 
Fic, 1. — Salivary gland of Holorusi bigi A cross-section of gland of larva; 2, cross- 
$ p : 11 Advanced 
on being 
are regularly circular or elliptical (in optical plane) and sharply 
delimited by a nuclear membrane. The chromatin is rather 
massed together and stains strongly. The cytoplasm of the 
cells is evenly granular and the cell outlines well defined 
(Fig. 1, 4). Ina pupa not more than twenty-four hours old a 
marked degeneration of the cells has occurred. The cytoplasm 
is distinctly vacuolated, and in a pupa a day or two older the 
cytoplasm is spongy, the cells have lost their shape, the nuclei 
have lost their membranes and are showing other degenerative 
characters (Fig. 1, B). No phagocytes appear. The degenera- 
tion or histolysis of the larval tissues of Holorusia is accom- 
plished thus without the interference of phagocytes. The pupal 
condition is characterized by no such extensive breaking down 
