482 Miscellaneous. 



a nervous system of its own which is of merely i)rovisional import- 

 ance and which already begins to develop in the latter part of the 

 embryonic period. At the anterior pole, which is distinguished by 

 the tuft of cilia, a delicate system of fibres was observed by Burj-, 

 who conjectures that it is possibly nervous. The apparatus proves 

 to be of a highly complicated character. The cells of this region, 

 which we may term the apical pit, consist of sense-cells and ixndiffe- 

 reutiated supporting-cells. Both kinds of elements are rod-shaped, 

 and their nuclei lie at somewhat variable altitudes near the inner 

 ends. These latter appear to be blunt in the case of the supporting- 

 cells, but in the sense-cells, on the contrary, are drawn out into a 

 fine process which penetrates into the layer of the nerve-fibres. The 

 nerve-fibre layer is of considerable thickness at the apex, but 

 diminishes very rapidly towards the periphery ; it is only on the 

 ventral surface that a powerfully developed cord of fibres extends 

 on each side of the vestibular invagination far into the posterior 

 section of the body. Under the apical pit the layer of fibres is 

 bounded towards the primary body-cavity and the mesenchyma cells 

 by a basement membrane, Avhich appears at a very early stage in 

 the embryonic development. Even before the cells of the apical 

 pit had attained their definite histological character, as supporting 

 and sense-cells, numerous ectoderm cells separated from their con- 

 nexion with the epithelium and wandered into the depths, to become 

 transformed into ganglion cells, which lie above and between the 

 layer of fibres. Isolated ganglion cells are also embedded in the two 

 ventral longitudinal nerve-trunks. 



Soon after the attachment of the larva the entire nervous system 

 disappears, and it is not until much later, some two to three weeks 

 after the attachment takes place, that there appears at the oral disk 

 — which proceeds from the vestibular invagination — an extremely 

 delicate nerve-ring, which is identical with the apparatus described 

 by Ludwig as the sole nerve-centre of the adult form. It is of 

 exclusively ectodermal origin, and beside the fibres scattered 

 ganglion cells can be distinguished. I have not been able to follow 

 up the origin of the second and third nervous systems of the adult, 

 which were discovered by Carpenter and Jickeli, since in the oldest 

 of the larvae examined by me the rudiments of them were not yet 

 visible. — ZoologiscJier Anzeiyer, xv. Jahrg., no. 404 (Oct. 31, 1892), 

 pp. 391-393. 



On Deglutition in the Synascidiae. By S. Jouebain. 



The mechanism of deglutition in the Composite Ascidians, by which 

 I mean the Ascidiae Sociales of H. Milne-Edwards, is still imper- 

 fectly understood. 



Several naturalists, applying to these animals what Hermann Fol 

 found to be the case in Doliolum,, have supposed that the nutritive 

 particles follow the groove of the endostyle. This groove secretes 

 a cylinder of mucus which agglutinates these particles and which, in 

 consequence of the action of the vibratile cilia with which the groove 

 is lined, descends towards and enters the stomach. 



