110 W. BLAXLAND BENHAM. 



primary, bar; (a) the visceral vessel at the pharyngeal end of 

 the bar ; [b) the somatic vessel in the apical notch of the rod; 

 and (c) the skeletal vessel inside the rod : the last two anasto- 

 mose here and there. 



5. The cavity of the rod is ccelom, is lined by flat cells, 

 and contains this skeletal blood-vessel. 



6. The outer wall of this ccelom is homologous with the 

 extra-coelomic cutis (Spengel's basement membrane) of the 

 primary bar. 



7. The septal membrane and the rod are mesoblastic, and 

 the nuclei of the cells forming them are here recorded for the 

 first time. 



c. The Observations of Recent Observers. 



I will now pass on to a brief survey of the various descrip- 

 tions and figures of the tongue bar of previous writers, copies 

 of whose figures are represented on PI. 6, and in the expla- 

 nation of these, the references whence the figures are taken. 

 Stieda, Langerhans, and Schneider saw no modifications of 

 the epithelium at the pharyngeal end of the bar. Lankester 

 was the first to observe this, and his figures represent more 

 accurately than do those of his successors, Spengel and Boveri, 

 the actual arrangement. As I have already pointed out, how- 

 ever, he missed the fact that the middle group presents two 

 rows of nuclei. This is equally overlooked by Boveri, while 

 Spengel's drawing is not quite clear on this point, and neither 

 of these latter indicate the much greater length of the nuclei 

 in this part of the bar. So far as the general shape of the 

 pharyngeal end of the bar is concerned, SpengeFs and Boveri^s 

 drawings show it fairly. Fig. 12 from Boveri is taken from 

 quite the upper end of the bar, hence the peculiar shape of 

 this end. Lankester is alone in regarding — as I believe 

 wrongly — the epithelium of the sides of the bar as in several 

 layers. Spengel points this out ; but he, like all my prede- 

 cessors, with the doubtful exception of Schneider and Langer- 

 hans, represents small round instead of oval nuclei here. 



The authors, as will be seen from the reproductions of 



