102 MCMURRICH. (VoL. XIV. 
masses. The large size of the chromatin granules, as compared 
with the microsomes, and their relation to the achromatic sub- 
stance throw doubt on this idea, however, and the doubt is 
confirmed by the behavior of the nuclei to the Biondi-Ehrlich 
stain. With this Korschelt found the microsomes to assume a 
red color, and the chromatin masses became green; in the Iso- 
pod nuclei the granules took the greenish hue, while the nucleoli 
became red. It seems that the granules of the Isopod nuclei 
are equivalent to the chromatin masses of the silk glands, while 
the nucleoli of the Isopod nuclei are not represented in the 
glands, and the microsomes of the latter do not occur in the 
Isopod nuclei. 
The granular arrangement of the chromatin is perhaps the 
most striking feature of these nuclei, and it is one which devel- 
ops early. In the embryos, up to the time when the formation 
of the digestive tract is completed, the nuclei possess the 
structure usually seen in embryonic tissues, but in individuals 
which have just left the brood pouch the transformation of the 
nuclear structure has already begun. In Fig. 9 is shown a 
nucleus from such a young individual; one sees the chromatin 
in the form of granules, scattered on the achromatic reticulum, 
and it is noticeable that in addition to several large granules 
numerous small ones occur. In other nuclei the number of 
small granules was much larger, and in specimens 4 mm. in 
length (Fig. 11) the granular arrangement was almost as fully 
developed as in the adults. I may state that I have not, in 
adult cells, been able to distinguish centrosomes or archoplasm 
spheres. 
III. 
In the epithelium of the ‘“midgut”’ of the terrestrial Isopods 
we have a tissue which possesses many peculiarities, the most 
striking of which is perhaps its ectodermal origin. As a result 
of this origin it is lined throughout its entire extent by a layer 
of chitin, which is destitute of pores, and must be regarded as 
exceedingly impervious. Can it be possible, then, that the 
“midgut” is, as so many of the authors who have written on 
the subject have supposed, an organ of absorption? Can we 
