their Organs of Respiration. 



245 



37f"f 



really divided into two halves by a furrow in which the trunks 

 of the blood-vessels lie ; and this structure becomes obvious 

 in some families where, as in Pyrosoma, the interspace is con- 

 siderable ; and is still more remarkably obvious in the S&dpae, 

 in which, in fact, the branchial vessels are not disposed on 

 the walls of the sac, but occupy the margin of two narrow 

 linear leaflets of very unequal lengths that lie across the 



cavity. These are 

 formed by a dupli- 

 cature of the inner 

 tunic, and the supe- 

 rior margin is gar- 

 nished with a close 

 series of little vessels 

 which run parallel 

 to one another in a 

 transverse direction; 

 a form and dispo- 

 sition which, says 

 Lamarck, has very 

 little analogy with 

 what is regarded as 

 the respiratory or- 

 gan in the Ascidiae 

 {Hist. Nat, vol. iii. 

 p. 114.); but which, 

 on the contrary, 

 Carus seems to think 

 is just the link that connects these with the bivalves, " appear- 

 ing to constitute the transition from the Ascidiae to the Tere- 

 dines, where there are two elongated branchial laminae above 

 the intestine and within the tubular cloak, to which the water 

 has access and egress by means of two tubes placed at the 

 posterior extremity of the body." (Comp. Anat., vol. ii. p. 147. 

 trans.) 



Let us, before proceeding, reflect a moment on that won- 

 derful diversity in the structure of the same organ here ex- 

 hibited to us in one class of animated beings : it is a fine 

 example, among many, of that variety in which the Creator 

 of all has seen good to indulge in the production of his works, 

 as if, to use the words of a favourite author, He " willed to 

 show those whose delight it is to investigate his works, by 

 how many varying processes he can accomplish the same 

 end." I see in it also a proof, that neither external and phy- 

 sical circumstances, nor self-born desires, have that great and 



r 3 



Of nthio Dibne Savigny. 



