Manchester Memoirs, Vol. I. (1905), No. \. 5 



fuses, so that a hollow, chitinous rod communicating with 

 the buccal cavity is formed. In each of these species the 

 chitinous rod is flat and fluted, so that in section it has a 

 wavy appearance (see Figs, i, 2, le.). In P. novae zealandiae 

 and O. oviparus the inner wall of the rod is thin, while 

 the portion adjacent to the attachments of the muscles is 

 much thicker.* 



The specimens of P. balfouri examined had these two 

 walls of equal thickness, as shown in the accompanying 

 figures. These walls are in all cases thick in the middle, 

 and gradually become thinner, as seen in transverse 

 section, towards their edges, where they join to form the flat, 

 hollow, chitinous jaw-lever. In some sections the rod has 

 a solid appearance, the two sides having collapsed. The 

 character of the epithelial pocket, into which the jaw-lever 

 fits, is the same in each species. It is made up of a single 

 layer of cubical cells containing large nuclei {^Fig. 2), 

 and is simply a deep pocket of the epithelium lining the 

 buccal cavity. In no section is the continuity of this 

 cellular layer broken, either at the edges or at the sides of 

 the chitinous rod. The ends of these epithelial pockets 

 are quite blind, and consist of a solid mass of epithelial 

 cells. The chitinous jaw-lever is also imperforate (except 

 in certain sections where the perforation is clearly an 

 artifact). 



To sum up, the continuity of the cellular layer of the 

 epithelial pocket, and the imperforate nature of the hollow, 

 chitinous jaw-lever, render the presence of tracheal struc- 



* The sections of P. novae zealandiae and P. balfouri were cut %ij. thick, 

 and stained with brazilin (4). This reagent stains the chitina deep, purplish 

 black, so that the thin inner wall is rendered perfectly visible. Unless this 

 thin inner wall is stained, it may be mistaken for an optical effect cau.sed by 

 the balsam and the inner wall of the epithelial pocket, consequently the jaw- 

 lever would appear to be a solid chitinous rod instead of a hollow chitinous 

 rod. 



