Novia SUDGUL OF THE TERRESTRIAL ISOPODS. 97 
AVERAGE LENGTH AVERAGE BREADTH 
LENGTH OF SPECIMEN. ap (ens oe (inne 
4 mm. 26.6 & 277 ih 
6 mm. 33-4 39-5 wu 
9 mm. 47-5 bt 54-7 
12.5 mm. 69.9 u 104.9 & 
We see from this that there is a gradual increase in the size 
of the cells in passing from the 4 mm. specimen to the 12.5 
mm. one. Whether this increase in the size of the cell is suffi- 
cient in itself to account for the increased length of the «“ mid- 
gut,” it is difficult to estimate, as I did not succeed in isolating 
the entire “midgut” in the smaller specimens, and therefore 
could not determine its length. If we take the length of the 
entire animal as the basis of comparison, a certain allowance 
for the stomodzeum and the rectum ought to be made, but how 
much I cannot say. However, even without making any allow- 
ance, the figures obtained by such a comparison have consider- 
able interest, and I give them for what they are worth. The 
length of the body of the smallest specimen is taken as the 
unit, and with it is compared the length of the body of each of 
the other specimens, and similar comparisons are made between 
the lengths of the cells of the various specimens and that 
of the cells of the smallest specimen, which are again taken 
as a unit. 
CoMPARISON MADE 
aa LENGTH OF Bopy. LENGTH OF CELLS. 
4mm. and 6mm. ie Sal RLS 
Acmme) | “)) 9) mm: Tesi 2s25 To:) 2.10 
4mm. “ 12.5 mm. 0B Bau Ei 2-0 
We find here, even without the corrections that should be 
made, evidence that the increase of length of the “‘ midgut ”’ is 
produced by an increase in the length of the cells which com- 
pose it, and not by the formation of new cells. 
With regard to the increase in the circumference, evidence 
is furnished not only by the measurements but also by simply 
