SHAPE OF THE NUCLEUS 601 
Folds in the nuclear membrane are found in a great variety 
of cells in addition to gastric epithelium in Amphibia. They 
occur in cardiac muscle in Man and Astacus (the crayfish), 
and also in the connective-tissue cells of the Testis in the 
latter species. In germinal epithelium they are especially 
common, not only in that of the Axolotl (PI. 23, fig. 10) 
but also in some mammalian tissues. But in the latter it is 
usually difficult to make sure that the structures one can see 
TEXT-FIG. 10. 
Portions of muscle-fibres from nymph of Phryganaea sp.— 
a caddis fly. In a the membranes of Krause can be seen running 
across the sarcoplasm and constricting the nucleus at regular 
intervals. In B only the nuclear constrictions are visible, the 
section passing outside the zone of myofibrillae. ui, Hensen’s 
line; MK, Membrane of Krause. 
in germinal epithelium are truly intranuclear folds, though it 
is interesting to note that undoubted incisions exist in the 
pathological cysts—Cystadenomata—which are derived 
from this epithelium. 
The nuclei of smooth muscle-fibres, after impregnation by 
the Cajal method for the Golgi-apparatus (Cajal, 1; Carleton, 
2), show a peculiar spiral peri-nuclear band which has been 
observed by Rio Hortega (11). After careful differentiation, 
iron haematoxylin sections show that this structure is not 
a thickened portion of the nuclear membrane but a series of 
usually rather irregularly arranged spiral folds. ‘Transverse 
