PHOLAS. 207 



employed, as its weight iu young subjects without great care 

 often causes ruptures, and from its density it does not pass 

 so freely as aqiieous 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 interlamiuar 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-laminae, 

 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 into 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 being killed, and 

 alcoholized to harden the fabric, and the contractive qualities 

 of alcohol are well known, had, when the moisture was 



