MR GOODSIR ON THE ANATOMY OF AMPHIOXUS LANCEOLATUS. 261 



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 RETZIUS, and is in accord- 

 ance with the type of formation in the class. 



Viewed as an entire animal, the Lancelet is the most aberrant in the verte- 

 brate 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 Mollusks. We have only to suppose the Lance- 

 let to have been developed from the dorsal aspect, the seat of its respiration to be 

 transferred from its intestinal tube to a corresponding portion of its skin, and 

 ganglia to be developed at the points of junction of one or more of its anterior 

 spinal nerves, and inferior branch of its second pair, to have a true annulose ani- 

 mal, with its peculiar circulation, respiration, generative organs, and nervous 

 system, with supra-cesophageal ganglia, and dorsal ganglionic recurrent nerve. 



As some fishes undergo metamorphoses after leaving the ovum, the question 

 naturally suggests itself, is the Lancelet an adult fish ? May it not be the young 

 of some fish in one of the stages of growth ? The uniformity of every specimen 

 of it hitherto described, and the peculiar toughness and firmness of its tissues, 

 appear to be decisive of its being a perfect animal. 



In regard to the zoological position of Amphioxus, Mr YARRELL was correct in 

 giving it the lowest place in the class of fishes ; but if the details of its structure, 

 and the anatomical considerations which this paper contains, be correct, the genus 

 can no longer be retained in the same family with Petromyzon and Myxine, but 

 will assume an ordinal value in any new arrangement of the class. 



If genera allied to Amphioxus are at present in existence, they are probably 

 not numerous ; but in the ages which have passed since the development of ani- 

 mal forms commenced, a-branchiated fishes may have been more common ; and 

 the paleontologist, when his attention is directed to the subject, may probably be 

 able to refer some anomalous organic remains to extinct fishes of this order. 



* Report of the British Association, 1840. 



