458 E. RAY LANK:ESTER and ARTHUR WILLEY. 



club-sliaped glaud. They have been figured by Hatscliek, who 

 has described the pr?eoral pit as cousisting of a ciliated de- 

 pression and a short glandular tube, and has traced to this 

 structure the thickened ciliated epithelium which is found ou 

 the inner face of the oral hood of the adult forming there — the 

 so-called " Rader-organ/' 



Hatschek, in his important memoir in the ^Arbeiten a. d. 

 Zool. Institute d. Univ. Wien,' vol. iv, 1881^ does not figure 

 any larva later than one with a single gill-slit. In one of the 

 wall-plates of Leuckart and Nitsche, however, received by us 

 during the progress of this work, there are a number of figures 

 of later stages, which have to some extent assisted us in arriving 

 at an understanding of the later unillustrated note by Hatschek 

 (' Zoolog. Anzeiger,' 1884, p. 517). None of the published 

 figures exactly coincide with our younger larva as to age, and 

 our later larva is even less closely represented in the diagrams 

 above mentioned, so that the figures we are able to publish are 

 new, and will probably be of service to naturalists. The club- 

 shaped gland, though figured by Hatschek and earlier observers, 

 has not been described. It is remarkable for its early develop- 

 ment (observed by Hatschek), and for the fact that it seems to 

 entirely disappear in the adult without leaving any trace. The 

 gland is a sac with a large lumen. It lies obliquely on the 

 right wall of the buccal cavity, and, bending round below, 

 tapers to a narrow canal as it rises on the left wall of the 

 buccal cavity, where it opens just below and external to the 

 margin of the mouth. In the younger of the two larvae 

 figured the club-shaped gland has no internal opening; it ends 

 blindly just below the notochord. But in the later stage 

 (drawn in figs. 4, 5, 6) the gland has acquired an opening into 

 the cavity of the mouth. This orifice is placed at the opposite 

 end of the glandular sac to its external opening (PI. XXIX, 

 fig. 5 ; and PI. XXX, fig. 5, int. a., and fig. 2, ext. a.). 



By the side of and anterior to the club-shaped gland is a 

 tract of modified epithelium of the buccal cavity of about twice 

 the breadth of the gland itself, and divided by a median clearer 

 space into two parallel tracts. This strangely-placed group of 



