STRUCTURE OF THE PHARTNGEAL BARS OF AMPHIOXUS. 5 



further from the base of the cell. The nuclei are elongated 

 and oval ; they are placed much closer to one another than my 

 figure represents, and as they stain deeply are very conspi- 

 cuous. In thick sections it is difficult to determine whether 

 one has to do with a single row of very elongated cells (as 

 Lankester believed), or with several rows of them; this diffi- 

 culty is emphasised when the sections are not accurately 

 transverse. But in thin sections, successfully cut, it is easily 

 seen that the nuclei are arranged as I describe them. 



The cells to which these nuclei belong are, therefore, as 

 long as the epithelium is thick ; they are very narrow peri- 

 pherally and swollen at the nuclear level, producing the flask- 

 shaped appearance of the whole group. These cells carry 

 cilia which are considerably longer than those carried by the 

 lateral groups of cells at this inner end ; and it is curious that 

 of previous observers, only Spengel and Boveri have noted 

 this special bundle of cilia. The free ends of the cells are pro- 

 vided with a very finely striated border, which comes out well 

 in cochineal preparations, but which is riot differentiated by 

 other stains used. 



Each lateral group of nuclei consists of a single row curving 

 downwards from the central group towards each side, some- 

 what in the way represented by Lankester; but I find that 

 these nuclei, which are long and narrow, are not arranged 

 quite in the fan-shaped manner represented by him. 



The cells containing these nuclei carry quite short cilia 

 entirely overlooked by Spengel and Boveri, and their free 

 ends are not provided with a striated border. The shape of 

 this inner end has been very variously represented, as the 

 copies of previous figures on PL 6 will show. 



The side of the bar presents some four or five rows of small 

 nuclei forming a broad band, about two thirds the whole width 

 of the epithelium. These nuclei are not circular, as most ob- 

 servers have represented them (owing to the obliquity of the 

 section, as I know from experience), but are oval, with the 

 long axis directed vertically to the plane of the surface. 

 Langerhans appears to have noted their oval shape. 



