260 THE HARMONIES OF NATURE. 



water had been made to pass through them in two opposite 

 directions. 



In the sharks and rays we find a different arrangement of the 

 gills, as here the branchial arches are not freely suspended in 

 the branchial chamber, but stretching across its cavity divide it 

 like so many bulkheads into five distinct compartments, whose 

 walls are tapestried with the innumerable folds of the branchial 

 membrane. The water entering the mouth does not escape 

 through an opercular opening, but through five distinct orifices 

 situated on each side of the body. 



In the lamprey and hag the branchial apparatus on each 

 side is similarly divided into seven compartments ; but these 

 fishes, from the peculiarities of their 

 habits, require another modification in 

 the construction of the organs of respira- 

 tion, seeing that while they rest fixed by 

 their suctorial mouths to the surfaces of 

 stones or other foreign bodies, or while 

 they are compelled to remain with their 

 heads deeply plunged into the flesh of the 

 prey upon which they live, the admission 

 of water into the mouth and its subsequent 

 expulsion through the gill-openings (i) 

 would in their case be impracticable. Here, 

 therefore, a framework of cartilaginous 

 pieces forms a kind of elastic thorax around 

 the regions of the body where the bran- 

 chia? are situated, and by its alternate 

 movements of contraction and dilatation 

 perpetually sucks in the water and again 

 expels it through the external openings. 



In the myxine or hag these orifices are 

 moreover situated very far back in com- 

 parison with the usual situation of the gill- 

 O p en i n g Sj so that the creature is able to 

 a cavity communicating with respire while deeply plunging into the 



the respiratory sacculi of r J 



both sides. soft parts ofits unfortunate victim. Thus 



even in this meanest and lowest of all vertebrate animals we 

 find a remarkable adaptation of its construction to its wants, 

 and the proof that it has been as well taken care of by the Creator 

 as the highest members of its class. 



