151 f : 



MISCELLANEOUS. 



On the Anatomy and Histology of Branchiostoma lubricum, Costa 

 (Amphioxus lanceolatus, Yarrell). By M. J. Marcusen, of 



St. Petersburg. 



It might be thought that, after the investigations of Johannes 

 Muller and Quatrefages, there would be little to discover in the ana- 

 tomy and histology of this curious animal. But as it is now nearly 

 twenty years since these naturalbts published their memoirs, and as 

 since that time the means of research have been greatly improved, 

 during my residence at Naples I submitted the Branchiostoma to a 

 new examination, which has led me to the discovery of many facta 

 unknown to my predecessors, and enabled me to rectify several of 

 their rosnlt?. 



\ i:rtebral system. 



1. Dorsal Chord. — This is composed, as is well known, of a sheath 

 and contents. The latter were described by Goodsir and Muller as 

 consisting of a iibrous mass separable into disks. Quatrefages haa 

 denied the existence of the latter, and declared that the dorsal chord 

 is composed of juxtaposed cells, of which he has given figures. 

 According to my investigations, the cells do not exist ; and May 

 Schultze has also been unable to discover them. The dorsal chord 

 separates so readily into disks that they may be recognized even in 

 the living animal, but the separation is not complete. The dislu are 

 very thin, their thickness being only ^^th mill., and they are 

 united on the two sides by a very delicate substance, which issues 

 from the two surfaces at a great many {wints, so that in separating 

 one disk from its neighbour the unitmg membrane is torn, and its 

 d6bris present a net-like appearance upon the surface of the disk, 

 giving the latter an aspect of being composed of cell.<». In reaUty, 

 however, there is only a smooth disk, of which the surface is covered 

 with shreds of the uniting substance. Sometimes we may see in the 

 substance of the disk itself several perfectly transparent nuclei. 

 Perhaps the network of the uuiting substance may represent the 

 remains of cells ; but otherwise there are no cells in the dorsal chord 

 of the Branchiostoma, 



2. Buccal Cartilage. — This cartilage, as well as its processes 

 which form the skeleton of the buccal cirri, is also composed of a 

 mass which separates readily into disks ; but here the cells of which 

 these are composed have not entirely disappeared, for nuclei of larger 

 or smaller size are seen granulated into an intercellular mass. 

 Quatrefages saw this ; but he believed he saw cells without nuclei, 

 with their outlines contiguous — which do not occur. 



NERVOUS SYSTEM. 



Quatrefages has the credit of having described the distribution of 

 the nerves better than his predecessors ; and it is also to him that 

 we owe the interesting observation that the central nervous system 

 is composed of a series of inflations corresponding with the origin of 



