Nomi) MUDGUL\ OL THE TERRESTRIAL TSOPODS. O11 
tion is in the plane a 6 of the diagram, one looks down on the 
edges of the depressions of the cuticle between the adjacent 
domes, and so obtains an optical transverse section of the cuti- 
cle, while by focussing lower, as in the plane c d of Fig. 1, the 
lower edges of the depressions of the cuticle are passed and the 
cells appear less distinctly separated. 
I wish to insist upon this difference in the appearance of the 
optical section according as the focus is high or low, since I 
believe that a failure to note the true significance of the appar- 
ent boundaries has led certain authors to an erroneous interpre- 
tation of one of the peculiarities of the epithelial nuclei. To 
this I shall return later on, but here I may point out that Car- 
noy (84) has evidently fallen into the error. Thus he says, “En 
dehors du protoplasm a la limite des cellules, se dessine une 
zone brillante, divisée en son milieu par une ligne plus sombre. 
Celle-ci n’est autre chose que la membrane primaire, commune 
aux cellules juxtaposées; tandis que les lamelles blanches qui la 
bordent représentent la membrane secondaire, qui est propre a 
chaque cellule et s’est formée plus tardivement.”’ As a matter 
of fact, Carnoy’s ‘“‘membranes secondaires” (see Fig. 2, ch) 
are simply the layers of chitin as they dip down between the 
domes of adjacent cells, while his ‘‘membrane primaire”’ is 
probably merely the interval between the two folds of chitin ! 
The distinctness of the epithelial cells being then only a 
superficial appearance, is it to be believed that the lack of 
distinctness towards the bases of the cells is due to the actual 
continuity of the protoplasm throughout the gut? Huet (ss) 
supposes that such a continuity exists, and I believe that the 
evidence presented by sections bears out his supposition. Never 
have I seen in preparations from adult individuals any such dis- 
tinct and regular cell boundaries as are figured by Ide (92), but 
in those situations where, in sections, one would expect to find 
the cell walls, one sees only the supportive fibres, and these, 
not being lamellz, allow the protoplasm of adjoining cells to 
pass between them and become continuous. 
In preparations from young specimens, however, a distinct 
separation between adjoining cells seems to be present, and it 
is probable that the individuality of the cells is present in young 
