STRUCTURE OF GLANDULAR VENTRICLE OF SYLLIS. 475 
interior a core of granular nucleated protoplasm, which, the 
enveloping differentiated striped muscle being overlooked, 
might very naturally be regarded as being of glandular nature. 
Like all the other organs in the perivisceral cavity, the 
gizzard of the Syllide (figs. 2 and 3) is enclosed in a layer of 
the peritoneal membrane. Beneath this a stratum of fine 
longitudinal and circular fibres of the ordinary non-striated 
muscle arranged in three layers. Then follows the middle 
layer (6), which is by far the thickest and contains the sup- 
posed glands, and, internal to this again, is a thin internal 
fibrous (muscular) layer with circular and longitudinal fibres 
followed by the thin epithelium of non-ciliated columnar cells, 
and, finally, the delicate chitinous cuticle. The thick middle 
layer contains in its outer portion a series of thin annular 
bands of non-striped muscular fibres (figs. 2, c, and 3, e), which 
are flattened in the direction of the long axis of the organ, 
These annular bands are arranged at regular intervals along 
the whole wall of the gizzard, and it is to their presence that 
is due the appearance of regularly arranged transverse lines 
which has been already repeatedly referred to. Ina transverse 
section the middle layer is found along two lateral lines (seen on 
a surface view as the two light longitudinal lines) to be repre- 
sented only by a raphe formed by the annular bands of non- 
striped muscle anastomosing with the inner muscular layer. 
The intervals between these ring-like bands are occupied by 
the ends of rows of radiating columns. In the species which 
I shall temporarily designate as Syllis a,! these columns (fig. 
3, 6) are ~>th of an inch in length, broadest at the outer end 
and gradually narrowing towards the inner extremity. The 
average breadth is ;+;th of au inch. Between the fibres 
extends finely fibrous matter with nuclei, but this cannot be 
said to form anything that can be called a distinct sarcolemma 
on the surface of the fibres. The outer portion of the fibre is 
squarish in transverse section, the inner end rounded. Along 
the axis of the fibre runs a core of finely granular protoplasm 
1 All the species referred to in this paper are Australian members of the 
restricted genus Syllis. 
