210 PHOLADID.E. 



tubes, that is one inhalant and branchial and another ex- 

 halant and anal, or by what I term supposititious ones ? The 

 former position I think I have proved in the Pholades, by 

 showing that there is no effective communication between the 

 two chambers ; and in the Anomice and Ostrece, that the latter 

 condition of the currents is imaginary, appears to be the 

 most correct view. It may therefore be considered that in 

 the Bivalves, whatever -modification their siphonal mechanism 

 may present, all are subject to a general law of the water 

 being expelled from the same siphon or channel at which it 

 entered, aided by the pedal gape and pedal aperture where 

 they exist; and in the Anomice and Ostrete, in wliich these 

 organs are rudimentary or entirely wanting, the water is 

 simply received and expelled through the ventral range, and 

 not by an imaginative inhalant and exhalant regular current, 

 effected by cilia. 



The remainder of Messrs. Alder and Hancock's paper re- 

 quires no further notice except a few words on their concluding 

 experiment showing how the colouring matters collect in the 

 neighbourhood of the buccal aperture. I have observed these 

 appearances, but I am of opinion, that in an animal cut up 

 from stem to stern, with the so-called in-current, as they 

 admit, annihilated, little dependence can be placed on the 

 action of the gill-laminse floated in a shallow vessel, to account 

 for the colouring matters seen at its oral termination. And 

 I cannot understand the hydro-pneumatic statics of these 

 gentlemen, nor the position agreeably to their theory, that 

 " a tendency to form a vacuum " in the anal chamber and 

 interbranchial tubes is effected by the " flowing out " of the 

 water from the ex-current siphon, combined with ciliary 

 agency, which actions, they add, are the foundation of their 

 " correct answer to this question : How is the matter, divided 

 into such minute particles, collected on the surface of the 

 gills?" 



But a fallacy with respect to a tendency to form a vacuum 

 seems to present itself, as in this case a flowing out involves 

 the idea of a flowing in, which militates against the vacuum, 

 for the fact is, that with the outflow there is in their theory a 



