PEOFESSOTC HYim/s ANATOMICAL NOTES. 310 



are also provided with a cocldca hranchialis, to which, the organ 



described in Lutodeira, is, in its form, structure and uses, quite 

 similar. 



I may add that a few genera of the Salmones (Cuv.) or rather Cha- 

 racini (Miill.) viz. Prochilodus and Citharinus, also possess an acces- 

 sory respiratory organ, well supplied with nerves from the Vagus ; it 

 is situated above their gill chambers, and is either a straight blind 

 chamber, or has a curved sac-like form, in both cases receiving venous 

 blood from the heart, and returning red blood to the base of the 

 aorta. My friend, Professor Kner, a short time since, showed me 

 the same organ in Anodus. 



The following peculiarities in the structure of the gills of 

 Lutodeira are unique, no other clupeoid or characine fish affording a 

 trace of them : — 



1st. Each interspace between the branchial arches is divided into a 

 superior and inferior compartment by a short, strong and non-elastic 

 ligament, which unites the articulations of the basi- and cerato-branchial 

 bones (Owen) of each arch, with the like articulations of the same 

 bones, opposite to them. The branchial arches therefore cannot be 

 divaricated from one another, and their interspaces, the branchial 

 clefts, cannot be so much dilated as in other fish, but they remain 

 permanently in a state of extreme narrowness, and the current of 

 water which passes through them, must necessarily be very small. 



2nd. The cartilaginous combs, or fringes, attached to the concave 

 borders of the branchial arches, are set in two rows on each arch ; these 

 two rows are likewise divergent, so that the tips of the fringes of the 

 outside row of one arch, meet the tips of the fringes of the inside 

 row of the next one. The tips of each pair of fringes firmly coalesce 

 and cannot be separated without breaking them. Each branchial 

 cleft is therefore bridged over by a succession of gothic arches, 

 equal in number to the cartilaginous filaments in every fringe, and 

 there is no free passage for the current of water. The w r ater is, 

 therefore, it may be said, filtered through the coalesced fringes, 

 whose tips are directed towards the mouth, and, whatever may be 

 the amount of heterogenous particles in the water, they must be with 

 certainty caught between the pallisades, just as a fish is caught in a 

 net ; the surprising length, fineness and delicacy of the respiratory 

 branchial lamella? on the convex edges of the branchial arches, and 

 the excessive richness of their capillary net-work of vessels, are such 

 as fully to account for all these elaborate guards against mechanical 

 injury to so frail an organism. 



3. On a peculiar arrangement of the Gill chamber in Poly acanthus. 



This fish, one of the Labyrmthida>, presents a very peculiar ar- 

 rangement of its gill chambers. 



VOL. I. — ]S T . H E. 2 T 



