SHAPE OF THE NUCLEUS 593 
between the centrosome and the nuclear membrane: these 
are due to other causes and will be referred to later. And, 
finally, similar appearances can be seen in the nuclei of the 
interstitial cells of the testicle of Rana esculenta, the 
nuclear membrane here being pitted by the lecithin globules 
in the cytoplasm. 
Sometimes the inclusions are localized in a particular area 
of the cytoplasm. This may give rise to a peculiar deformation 
of the nucleus such as is depicted in Pl. 23, fig. 6, which illustrates 
a cell from the hepato-pancreas of the isopod crustacean 
Oniscus. Here the nucleus at the basal, i.e. attached, 
TEXT-FIG. 2. 
Cell from pronephros of a 3mm. larva of Triton alpestris. 
Note constriction of middle of nucleus due to pressure from 
Tonofibrillae, TN. 
pole of the cell is strikingly indented by large cytoplasmic 
clobules of a lipoid nature. It follows from this that nuclear 
deformation can be produced by relatively fluid bodies. 
Another instance of nuclear shape being modified by cyto- 
plasmic structures is afforded by the intestinal epithelial cells 
of the same species. By appropriate staining methods (see 
Pl. 24, fig. 3) fine fibrils lying in the cytoplasm around the 
nucleus can be distinguished. They run from the basement 
membrane to the cuticle, apparently function as an intra- 
cellular skeleton, and may be termed Tonofibrillae after 
the French ‘ Tonofibrilles ’. 
We have also observed a similar condition in cells from the 
excretory tubules of larvae of Triton as shown in Text- 
fig. 2. 
In those muscles which are characterized by cross-striation 
