now DOES THE PHOLAS BREATHE? 87 



exit, is unequivocal.* Look at the orifice of the upper 

 tube, what a beautiful arborescent fringe encircles it ! 

 You may see a picture of it in Mr Gosse's Rambles on 

 the Devonshire Coast very well delineated. "The tentacular 

 filaments," he says, "are numerous, each forming a little 

 tree with pinnate branches, bearing no small resemblance 

 to the flower of feathery branchiae that expands round the 

 mouth of a Holothuria. These branched tentacles are ordi- 

 narily bent down across the mouth of the tube, the long- 

 est of them just meeting in the centre ; alternating with 

 these are placed others of similar structm-e but inferior size ; 

 and the interspaces are occupied by others smaller still, and 

 simply pinnate ; so that when the whole occupy their or- 

 dinary transverse position, the smaller ones fill up the 

 angles of the laro-er, and the branches of all form a network 

 of exquisite tracery, spread across the orifice, through the 

 interstices or meshes of which the current of entering 

 water freely percolates, while they exclude all except the 

 most minute floating atoms of extraneous matter." 



The boatman has just called to say the boat is ready, and 



* This disputed question has been finally settled by the investigations of 

 Messrs Alder and Hancock, who find the communication takes place through 

 minute apertures between the meshes of the gills themselves. " Each of the 

 gill-plates consists of two laminfE united at the ventral margin, and likewise 

 attached to each other in transverse lines running across tho gills throughout 

 their whole extent, and forming, in the interspaces, a series of parallel tubes 

 which open into the dorsal chamber, and are thus in communication with the 

 excurrent sijihon. The minute reticulated blood-vessels of the branchial 

 larainse forming the walls of these tubes, are found, when examined by a high 

 power of the microscope, to be open between the meshes, which are minutely 

 ciliated, allowing the passage of the water into the tubes, and from thence 

 into the anal chamber." — Rejwrt of British Association, 1851 ; Sections, p. 7r>. 



