148 



HARDWICKE'S SCIE N CE-GOjSSlP. 



[July 1,'1869. 



illustration (Fig. 114) is taken. I scarcely need pre- 

 mise, that water is supplied to the gills through the 

 mouth as in other fishes, when the creature is not 

 adhering to any foreign body by its mouth. 



" In the Lamprey the organs of respiration have 

 seven external openings on each side of the animal ; 

 these lead into tlie same number of separate oval 

 bags placed horizontally, the inner membrane of 

 which is constructed like that of the gills in fishes. 

 There is an equal number of internal openings 

 leading into a tube, the lower end of which is closed 

 and the upper terminates by a fringed edge in the 

 oesophagus. These bags are contained in separate 

 cavities and inclosed in a thorax resembling that of 

 land animals, only composed of cartilages instead of 



up the cartilages and the pericardium. In the 

 La?npern the arrangements are the same, only the 

 cartilages of the thorax are so weak as to appear 

 like ligaments, and the pericardium is mem- 

 branous." 



Some further details are given by Yarrell : — 

 " When the Lamprey is firmly attached, as is com - 

 monly the case, to foreign bodies, by means of its 

 suctorial mouth, it is obvious that no water can pass 

 by that aperture from the pharynx to the gills ; it is 

 therefore alternately received and expelled by the ex- 

 ternal apertures. If a Lamprey while so attached to 

 the side of a vessel, be held with one series of aper- 

 tures out of the water, the respiratory currents are 

 seen to enter by the submerged orifices, and after 



< e 



Fig. 115. Vertical section of the Head of the Lamprey (Petromi/zon marinus), natural size. 

 J. D. McDonald, M.D., F.R.S., ad Nat. deli., May, I869. 



ribs, and the pericardium, which is also cartilaginous, 

 is fitted to its lower extremity like a diaphragm. 

 The water is received by the seven lateral openings 

 on each side of the animal into the bags which 

 perform the office of gills, and passes out by the 

 same orifices. The form of the cavities being fitted 

 to allow the water to go in at one side, pass round 

 the projecting parts, and out at the other. A part 

 of the water escapes into the middle tube, and from 

 thence either passes into the other bags, or out into 

 the oesophagus (?) There is a common belief that the 

 water is thrown out of the nostril ; this, however, 

 is unfounded, as the nostril has no communication 

 with the mouth. The elasticity of the cartilages of 

 the thorax admits of the water being received, and 

 it is expelled by the action of the muscles drawing 



traversing the corresponding sacs and pharynx, to 

 pass through the opposite branchiae, and to be for- 

 cibly ejected therefrom by the exposed orifices." 

 The wording of this passage might lead one to 

 suppose that the water received by the apertures of 

 the right side was invariably expelled by those of 

 the left, and vice versa; but this is not the case ; 

 the water may be supplied to the left side from the 

 right, if the animal is forcibly retained in an un- 

 natural position, and it will be expelled partly by 

 the apertures held above water, but also by the 

 submerged apertures 'by which it first entered; 

 there is no such crossing of currents as the text 

 seems to imply. I must venture, in all humility, to 

 take exception to Sir Everard's statement, that the 

 water which has passed from the gill-chambers into 



