32 
rent aspect. Instead of a thin continuous chitine layer with the 
spiral ribs (tænidia) presenting themselves in cross section as square 
or semicircular outgrowths from it we find here the chitine wall 
with unbroken parallel sides, the section of the wall itself presen¬ 
ting a transversal striping. Stained 
with hematoxyline and eosine some 
of the stripes appear with a deep 
purpie tint, absorbing both colouring 
matters equally well, the remaining 
stripes show only a very faint pink 
tinge from the eosine. By exami- 
nation with high power we find this 
pink part forming not only rather 
narrow stripes alternating with the 
broader purpie ones, but also an 
apparently continuous outer (distal) 
layer of the whole air-bladder. But 
in reality this layer is not quite 
continuous, it is formed by the wide- 
ning of each of the narrow stripes 
beyond the distal end of the purpie 
stripes so as to form a more or 
less rounded head which generally 
abuts against the two neighbouring 
heads; the limit between them is 
always seen as a faint dark line, 
and not unfrequently they are sepa¬ 
rated from each other by a narrow 
interspace; but perhaps this is only 
an artificial product due to a shri- 
velling of the tissues in alcohol. The 
distal ends of these heads together form an undulating line bor¬ 
dering on the epithelial sac. — The purpie stripes are IV 2 —3 times 
as broad as the pink ones, their distal end is convex, the proximal 
end slightly convex or straight, forming together with the proximal 
end of the pink stripes a slightly undulating or straight line. 
These stripes are broadest and most distinet in the ventral wall 
of the air-bladder, somewhat narrower, but still very distinet in the 
B 
Fig. 4. Longitudinal seclions of the walls 
of the sacs of the lake larva. A: section 
of the ventral wall; dimensions: Total 
thickness38,0 u, chiline21,l //, outerdark 
line 0,3 u, inner dark line 0.4 //, length 
of «heads» 3,5 u, breath of dark stripes 
2,1 //, grey stripes 0,7//. H : section of the 
dorsal wall; dimensions: Total 20,5 //, 
chitine 16,9 //, outer dark line0,2 //, inner 
dark line 0j3 //, <dieads» 1,8 //, dark stri¬ 
pes 2,8 //, grey stripes 0,7 //. C Part of 
wall towards the end; the stripes are 
narrowing and the «hpads» diminishing 
and finally disappearing. — Cam. lue. 
L. 8, W. compl. 5. 
