345 



tubes or fibres, and gave origin to the nerves in single roots only. 

 The nerves were all symmetrical, dividing into dorsal and ventral 

 branches. The second pair sent back a dorsal and a ventral branch, 

 to join the corresponding branches of the other nerves, along 

 the sides of the body, and along the bases of the dorsal and anal 

 fins ; from which distribution the author was inclined to believe, 

 that although the second pair in Amphioxus presented certain re- 

 semblances to the vagus, it was, in reality, the trifacial. 



The vascular system consisted of a straight abdominal vessel, 

 the branchial artery or heart, without any trace of valves or di- 

 vision into cavities. This vessel sent off lateral branches, which, 

 passing up on the internal surface of the intestine, along the ribs, 

 communicated by a capillary respiratory system of vessels with a 

 dorsal trunk or aorta. 



The intestinal tube was straight from mouth to anus, its ante- 

 rior half dilated, strengthened by ribs as described above, and its 

 entrance guarded by the hyoid rays. This dilated portion of the 

 canal received sea-water, as in the Ascidice, to act on the respira- 

 tory vascular ramifications on its internal surface, which is un- 

 doubtedly ciliated in the living animal. The digestive portion of 

 the canal is narrow, and presents not a trace of a liver, or of any 

 other assistant chylo-poietic viscus. 



As there was no trace of branchial fissures — as the ribs were 

 too numerous to be looked upon as true branchial arches (bran- 

 chial arches alternating with branchial fissures) — and as the other 

 organic systems were in the condition of those of an embryo before 

 the appearance of branchial clefts, the author was led to the con- 

 clusion that the Amphio.vus had never had, at any period of its 

 existence, branchial clefts; — that it was an animal which had 

 arrived at its perfect development before the branchial clefts had 

 appeared, and, consequently, with an undeveloped osseous and 

 nervous system, without a liver, and with an unilocular heart. 



After examining the generative organs, and other departments 

 of its anatomy, the author entered upon the consideration of the 

 zoological position of Amphioxus, which he observed could no 

 longer be ranked with Pftromyzon and Mi/xlne, but must take an 

 ordinal place in any new arrangement of the class. In conclusion, 

 he remarked, that although genera allied to Amphioxus might now 

 be rare, yet in the ages which have passed since the development 

 of organic forms commenced, Abranchiated fishes may have been 

 more common, and may yet afford subjects of research to the 

 pala'ontologi^it 



