STRUCTURE OF THE PHARYNGEAL BARS OF AMPfllOXUS 99 



2. Langerhans. — " Zur Anat. d. Amphioxus lanceolatus," ' Arch. f. 



mikr. Anat.,' xii, 1876. 



3. Schneider. — ' Beitrage zur Vergleich. Anat. und Entwickel. der Wir- 



belthiere,' 1879. 



4. Lankester. — "Contributions to the Knowledge of Amphioxus lanceo- 



latus," 'Quart. Journ. Micr. Sci.,' xxix. 



5. Spengel. — "Beit. z. Kenntniss d. Kiemen des Amphioxus," ' Zool. 



Jahrbuch ' (Anat.), iv, 1891. 



6. BovERi. — "Die Nierencanalchen des Amphioxus," 'Zool. Jahrbuch' 



(Anat.), V, 1892. 



In addition to these, a bibliography relating to Amphioxus 

 will be found in Lankester's paper. 



A. The Tongue Bar. 



The tongue (or secondary) bar is usually distinguished from 

 the primary bar {a) in being supported by a tubular skeletal 

 rod in place of the double rod of the primary bar, {b) and in 

 being without any ccelom between the rod and the atrial epi- 

 thelium. It is unnecessary to describe the relations of the 

 bars to one another or to neighbouring parts of the animal, as 

 these matters have been fully described and illustrated by re- 

 cent writers on the subject. 



The structure of the bar is most readily seen in its transverse 

 sections, but such sections — accurately transverse to the bar 

 — are not so easily obtained; in sections transverse to the long 

 axis of Amphioxus, only one or two bars on each side of the 

 pharynx will be cut transversely, though in the pre-hepatic 

 region more bars are so cut, and still more are very nearly 

 transversely cut, than is the case posteriorly. But by varying 

 the obliquity of the plane of section to that of the long axis of 

 the body, I was able, ultimately, to obtain sections which cut 

 nearly the whole series of bars in any section almost accu- 

 rately at right angles to their length. 



It appears to me that this is most important, for the discre- 

 pancies in various descriptions and figures of the bar are doubt- 

 less due to the more or less obliquity of the sections. 



Another matter which must be taken into serious account is 

 the mode of preparation and the character of the stain ; for I 



