ABSTRACT
It may be thought that the structure of the pharyngeal bars of Amphioxus is sufficiently known, after the description by Lankester, and more recently by Spengel; but there still remains a certain amount of doubt as to some points in the structure of the tongue or secondary bar, although recent authors are in agreement as to the general structure of the primary bar. It is to the tongue bar, therefore, that I have more particularly directed my attention.
I have not observed the “muscle-cells” in the bar described by Rohon and by Langerhans, J. Miiller and Schneider.
Spengel mentions the presence of finely granular material in the canal of the hollow rod (loo. cit., p. 278).
This usually is due to the softer nature of the central part of this rod, and is not really a cavity : the rod presents irregularly concentric markings, as if shrunk, and is firmer externally.
Spengel gives a figure very similar to this one in pl. xvii, fig. 13, illustrating his paper.
This differentiation of the cilia round the bar may be compared with that occurring in the gill filaments of Lamellibranchs, and in the cirri of Bra-chiopods, where there are similarly bundles of long cilia, situated at the sides or angles, and shorter cilia elsewhere. The existence of a skeletal tissue in these cases is a further analogous resemblance.
It should be borne in mind, however, that Boveri did not pretend to describe the bars except in so far as they are related to the nephridia.
Stieda regards the granular substance in the centre of the rod (fig. 2, a) as an axial part of the rod itself.
