4 W. BLAXLAND BENHAM. 



liave noted in my series treated differently in both these 

 respects various differences due to shrinkage and such effects, 

 which suggest the cause of certain omissions by some authors, 

 and of wrong interpretations and other errors. 



I have found that Kleinenberg's fluid (picro-sulphuric acid) 

 is the preservative which produces less distortion than other 

 reagents. Cochineal stains, especially Mayer's alcoholic cochi- 

 neal, serves best for the demonstration of blood in the vessels 

 and for the examination of the skeletal tissues. 



Hsematoxylin is, of course, useful for the nuclei, but cochi- 

 neal gives better results in the case of cell-bodies. 



Some of the animals were stained in bulk ; in other cases 

 the sections were stained on the slide. 



I proceed now to a description of a transverse section of a 

 tongue bar, as elucidated by the examination of sections 

 treated in different ways, as well as of isolated portions of 

 pharyngeal walk 



Such a section is a narrow bar (about three times as long as 

 it is wide), presenting two ends and two sides : one end, the 

 Outer end, projects into the atrium, and is covered by atrial 

 epithelium ; the opposite end, or Inner end, projects into the 

 cavity of the pharynx, and is lined by hypoblast. The sides 

 are directed (roughly) anteriorly and posteriorly. 



The bar consists almost entirely of columnar epithelial 

 c e 1 1 s, the inner ends of which abut upon a membrane, the c u t i s 

 (I follow here Professor Lankester), throughout the greater part 

 of the bar; whilst at the outer end the cells rest upon the 

 skeletal rod, which I regard as merely a specialised part of 

 this cutis. 



The character of the epithelium, however, differs at the two 

 ends and at the sides. At the Inner or pharyngeal end the 

 nuclei are arranged in three groups, a central group and a 

 lateral group on each side, as Lankester was the first to point 

 out. The nuclei of the central group are arranged in two 

 more or less curved rows (as in fig. 1), but this arrangement 

 is due not to the existence of two layers of cells, but to the 

 fact that alternately the nuclei are situated nearer to or 



