STRUCTURE, ETC., OF PLEISTOPHORA PERIPLANETH. 619 
reason for this is to be found in the different shape of the 
plasmodia and the nuclei. ‘lhe plasmodia are thin and gene- 
rally leaf-like, while the nuclei are spherical, and hence 
undergo great deformation in drying on to the glass. 
2. The Malpighian tubules were cut up ina very small drop 
of filtered egg-white, and fixed either by exposure to osmic 
vapour or by immersion in boiling corrosive sublimate and 
absolute alcohol in the proportions 2:1. After osmic the 
coverglass was washed in water, after corrosive sublimate in 
water plus iodine, to precipitate the mercury, the film in each 
case being either first hardened by passing through the 
alcohols in grades of 10 per cent., or stained straightway in 
Delafield’s hematoxylin. The excess of stain was then washed 
out in acid alcohol, the film being finally mounted in xylol, 
or, preferably, alcohol, Canada balsam. Films fixed by the 
above method were also stained with Heidenhain’s iron- 
hematoxylin. Delafield’s hematoxylin gave, however, better 
results. Fixation with osmic vapour and corrosive sublimate 
gave practically identical results. The network of the nuclei 
of the cells of the Malpighian tubule is somewhat finer with 
osmic than with sublimate, but the difference is very slight. 
STRUCTURE OF THE VEGETATIVE STAGES OF PLEISTOPHORA 
PERIPLANETA. 
The trophozoites are amoeboid nucleated masses of proto- 
plasm varying from uninucleated specks of protoplasm, 
fig. 1, from 2—3 w in diameter to masses measuring in some 
cases 30 by 55 pw, and containing 60 or more nuclei (fig. 15). 
The protoplasm may be homogeneous and hyaline (figs. 1—6), 
or exhibit a marked foam-like structure, produced by the 
presence of a large number of small vacuoles (figs. 10, 39). 
Vacuoles of every size are of frequent occurrence. ‘The 
protoplasm of the smallest trophozoites possessing only a few 
nuclei is, as a rule, hyaline, that of the larger multinucleate 
