28 
THE VOYAGE OF H.M.S. CHALLENGER. 
filaments ; side by side with these fusiform cells, cylindrical forms occur, with a broad 
outer end, and an inner end produced into long tail-like processes not more than two in 
number. It was not found possible to trace these processes into connection with any 
other cellular elements. These elongate cells are not uniformly distributed below the 
epithelium, but occur in patches, which can be generally recognised by a more than 
usually deep stain ; frequently they converge towards the middle of the patch. Some- 
times they are found below an even surface of epithelium ; sometimes in ridges, which 
look like papillae, but which are probably only wrinkles produced by the contraction of 
the muscular oscular tube. Immediately below this outermost layer follows a tissue- 
complex which is somewhat difficult to interpret. Most conspicuous and lying nearest 
the surface are little roundish granular bodies, 0‘004 to 0‘005 mm. in diameter, with a 
nucleus and nucleolus, lying in distinct cavities of a stained material. They appear to 
be the most visible portion of cells which are extended into processes difficult to 
distinguish. Lying deeper are granular irregularly branching cells, which look like 
collencytes. Next to these follows the layer of concentric myocytes. Scattered 
irregularly through the tissue of the oscular tube are numerous oval cells about 
0'015 mm. in diameter, consisting of granules 0‘003 mm. in diameter, some of which 
stain much more deeply than others. 
The detailed structure of the layer of concentric myocytes is best made out in teased 
specimens mounted in glycerine. Each myocyte (PL XXXIX. fig. 9) is then seen as a 
fusiform thread-like cell, 0*4 mm. long by 0'0035 mm. thick; in the middle is an 
elongated oval vesicular nucleus, O'OllS by 0’003 mm., containing a minute nucleolus, 
and surrounded by granular protoplasm, which extends 0"04 mm. along the axis of the 
cell on each side of it. The rest of the cell consists of structureless stained material. 
Associated with the myocytes are abundant collencytes (PI. XXXIX. fig. 10) produced 
into very numerous branching thread-like processes, which unite among themselves into 
an intricate network which pervades the whole muscle. Not only do they unite with one 
another, but with the myocytes also, so that all the constituents of the muscular mass are 
in protoplasmic continuity. Though this structure is best made out in teased specimens 
it can also be traced in tangential sections (PI. XXXIX. fig. 5), appearing particularly 
evident at those places where the pillars of fibre from the cloacal chamber enter the mus- 
cular tube of the oscule; the constituent myocytes of these fibres diverge to the right and 
left on entering this tube, and thus render the collencytes readily visible. From the 
foregoing description it would appear not impossible that a communication extends from 
the subepithelial columnar cells, through the underlying collencytes, to the collencytes 
of the muscular mass, and thence to the myocytes themselves, and thus the stimulus 
provoked by a foreign body touching the sides of the oscule, might extend to the muscle 
and bring about its contraction. 
Cloacal Chamber . — The walls of this chamber (PI. XXXIX. figs. 1-4) are formed 
