45 



among naturalists. Some, like Agassiz, separate it entirely from all 

 other fishes, while Haeckel proposes to place it in a distinct division 

 of the Vertehrata, and Professor Semper removes it from the 

 vertebrates altogether. But Professors Owen* and Huxleyt, con- 

 sidering it to possess the rudiments of a skull and brain, with the 

 elements of a vertebral column, retain it among the fishes, and it 

 forms the first or lowest orders of their respective systematic 

 arrangements. 



In Amphioxus, which ranges from one and a half to two inches 

 in length, the vertebral column is notochordal throughout life, that 

 is to say, composed of a membraneous rod enclosed in cartilage, 

 and as there is no enlargement of the skull for the reception of 

 the brain, the animal tapers nearly equally at either end. 

 The skin is scaleless, lubricous, and so transparent that the 

 internal structure is visible, and the eyes are not more fully 

 developed than in the common leech. The mouth is vertical, 

 jawless, and suctorial, and is furnished with vil)ratile ciHa. The 

 laucelet possesses neither heart nor swimming bladder, and is 

 without ribs and even rudimentary Kmbs. In all other fishes 

 respiration is effected by means of water passing through the 

 mouth and escaping hy the gills, or their equivalents; in this 

 species it traverses the whole interior of the animal and escapes 

 by a special pore on the under surface of the body. 



+ Professor Goodsir, long ago, called attention to this 

 peculiar mode of respiration, and noticed the resemblance 

 between the enlarged phrangeal sac of Amphioxus and that of the 

 tunicated mollusks or sea-squirts. He considered the lancelet 

 also as allied to the annulosa, from the simple organization of its 

 respiratory and circulatory system, and M. Kowaleves'ky has more 

 recently traced a close affinity between this species and the early 

 stages of some Ascidians. Thus, in Amphiorcns are united 



* Anatomy of Vertebrates. Vol i. 



t Preliminary Note on tlie Structure of the Skull and Brain in Amphioxm 

 lameolatus. Proceedings of the Royal Society, 1874. No. 157. December. 



X Transactions of the Royal Society of Edinburgh. Vol. xv , pi 11 

 p. 259. ' f . 



