PHOLAS. 207 
employed, as its weight in young subjects without great care 
often causes ruptures, and from its density it does not pass 
so freely as aqueous fluids. Sea-water coloured by indigo 
or archil, or pure, is the proper injection, which must not 
be pushed beyond a full distension of the interlaminar tubes. 
The animal should be prepared in as natural a state as 
possible, and not be killed by any process producing sudden 
asphyxia, as immersion in hot water or alcohol; the first 
destroys tenacity in delicate tissues ; the second thickens and 
hardens them too much, and occasions lesions and fissures by 
contraction. There must be no lesions in the gill-lamine, 
except those that result from imperfections, which prevail to 
more or less extent in every animal I have examined—at least 
500; any solution of continuity at the junction of the gills 
with the excessively delicate membranes of the body will be 
fatal to success. 
If the experiment is thus conducted, no injection through 
the anal siphon will flow ito the branchial vault by the route 
of the interlaminar canals; the only moisture, if any, that can 
arrive there, may be a slight exudation, a proportionate one 
to the number of perforations and cracks in the membrane 
from laminar malformation, and of these only those which 
pass through into the interbranchial tubes. There may be in 
the 40,000 parallelograms in each gill, about twenty flaws or 
imperfections, and I reserve the possibility that all or most 
of these may arise from the manipulation of such delicate 
tissues. 
After all these incidents, how am I to explain the great 
discrepancy between the experiments of the northern na- 
turalists, illustrated by their “ 10,000 pores,” and mine, from 
the impossibility of causing fluids to issue from the inter- 
branchial tubes by percolation through the membrane on 
which the network of the blood-vessels is spread? But ’tis 
said, the sight is keener in the North than with us southrons. 
The only solution I can offer is a mere guess, that the animals 
operated on by these gentlemen, after bemg killed, and 
alcoholized to harden the fabric,—and the contractive qualities 
of alcohol are well known, 
had, when the moisture was 
