218 . " PKOF. HUXLEY ON THE ; 



unite in the median ventral line for the greater part of their 

 length, leaving only the abdominal pore open. 



Although the structure of AmpJiioxus has been investigated by- 

 many able observers * during the last forty years, a reexamination 

 of this singular animal, with which I first made acquaintance in 

 1846, has convinced me that some of its most remarkable morpho-- 

 logical features have hitherto escaped notice ; and I will take this 

 occasion of laying a summary of the chief results at which I have 

 arrived before the Linnean Society. 



Ampliioxus has hitherto been generally assumed to be a ver- 

 tebrated animal, which differs from all others in possessing a mere 

 rudiment of brain and of skull, and in being devoid of renal organs, 

 - It is quite true that AmpJdoxus has neither brain nor skull, if 

 we restrict the application of these terms to those particular 

 forms under which the brain and skull are met with in the higher 

 Vertebrata; but if we ask whether those regions of the cerebror 

 ■spinal axis, and of the axial endoskeleton, which are metamor- 

 phosed into the brain and skuH in the higher Vertebrata are, or 

 are not, represented in Ampliioxus, the answer must be, that these 

 regions are not only present, but that, in relation to the size of 

 the body, they are much longer than in any other Vertebrate, and 

 that, in this respect, as in so many others, Ampliioxus is the 

 counterpart of the embryo of the higher Vertebrate. 



The oral aperture of Amphioxus is surrounded by a series of 

 tentacula ; and the spacious buccal chamber is divided from the 

 branchial one by a curiously arranged valvular "velum" (the 

 " Franzen " of Miiller). Close to the anterior end of the cerebro- 

 spinal axis is the ciliated olfactory sac discovered by Kolliker; 

 and the pigment- spot, which represents the eye, coats the extre- 

 mity of the same part of the cerebrospinal axis. 



On comparing Amphioxus with the Lamprey, in its larval or 

 Ammoccetes condition, the cerebrospinal axis of the latter is seen 

 to be a mere rod, somewhat enlarged at its anterior end, where it 

 bears a mass of pigment representing the eye, and connected, by 

 a very short cord, with a single ciliated olfactory sac. The oral 

 aperture of the Ammoccetes is also surrounded by tentacles ; and, 

 as in Amphioxus, leads into a wide buccal cavity, which is sepa- 

 rated from the branchial sac by two remarkable folds, originally 



* I need only mention the names of Eetzius, Eathke, Miiller, Goodsir, and 

 Quatrefages. Within the last two years Stieda has published an elaboi-ate 

 paper on Amphioxus in the Transactions of the Academy of St. Petersburg. 



