392 ON THE ANATOMY OF AMPHIOXUS LANCEOLATUS. 



performing the respiratory function, like the vessels of the 

 branchial chamber already described. The development of 

 cardiac septa and of a liver follow closely, if they do not 

 accompany, the branchial fissures. The absence of such 

 fissures in the Lancelet sufficiently explains this deficiency of 

 parts usually considered essential to the vertebrated animal. 



Tor similar reasons, true renal and generative organs do 

 not appear in this animal. 



The double row of isolated generative organs are in the 

 normal position of their embryonic representatives, and not 

 more advanced in organisation than the Wolffian bodies 

 at their first appearance. How the contents of these ovisacs 

 or spermsacs are conveyed to the exterior, it is difficult 

 to say. If the abdominal opening described by Professor 

 Eetzius actually exists, it appears to me much more probable 

 that it is an opening, not into the branchial, but into the 

 peritoneal cavity, as in certain of the higher fishes, and that 

 it performs the double function of admitting sea-water for 

 peritoneal respiration, and for allowing of the exit of the ova 

 and sperm from the cavity of the abdomen, into which they 

 are cast from the glandular organs attached to its lining 

 membrane. This hypothesis, which I have had no opportunity 

 of verifying, gets rid of the difficulty in a satisfactory manner, 

 explains to a certain extent the observation of Eetzius, and is 

 in accordance with the type of formation in the class. 



Viewed as an entire animal, the Lancelet is the most 

 aberrant in the vertebrate sub-kingdom. It connects the 

 Vertebrata not only to the Annulose animals, but also through 

 the medium of certain symmetrical ascidise (lately described 

 by Mr. Forbes and myself),* to the Molluscs. We have only 



* Report of the British Association, 1840, and No. XII. of this volume. 

 An important observation, bearing on the affinities of the Ascidians and 

 Amphioxus, has recently been made by the discovery by M. Kowalevsky of an 

 axial cylinder in the tail of the Ascidian larva, which possesses almost the 

 same structure as the chorda dorsalis of Amphioxus (Mem. de l'Acad. Imp. de 



