330 w. A. HASWELL 
about 0-005 mm. The former are less numerous, mainly 
situated towards the outer end, but oceurrmg throughout the 
core to its inner extremity. ‘The smaller nuclei are extremely 
numerous, distributed fairly uniformly throughout the length 
of the core. In addition there are a comparatively small 
number of nuclei belonging to what appear to be distinet 
cell-elements with fine-grained cytoplasm embedded in the 
core. Surrounding the cortex is a layer continuous with the 
core at the longitudinal fissure, composed apparently of similar 
material, and containing an occasional nucleus: the imvest- 
ments of contiguous columns coalesce completely. 
Slightly less complex than Syllis coruscans are the 
cores in Trypanosyllis zebra. In this species the 
arrangement of the muscles conforms to type (3). The cores 
here consist of two kinds of material—an axial part, split into 
two in the perforated fibres, and a peripheral part. The former 
is loaded with rounded granules which are strongly coloured 
by haematoxylin ; the latter appears as a meshwork of delicate 
threads, prolongations of which pass into the substance of the 
cortex. Strands of granules similar to those in the central part 
of the core run longitudinally between the fibrils of the cortex, 
and the latter is enclosed in an investing layer which encloses 
similar granules. ‘The central part of the core contains numerous 
nuclei. 
In Syllis variegata (figs. 2 and 3), in which also the 
arrangement of the muscles conform to the third type, the 
core is greatly simplified. In the perforated columns it is 
split longitudinally into anterior and posterior halves which 
unite together only at the extreme outer ends outside the annular 
bands. ‘The substance of the core and the layer investing the 
cortex is a finely granular homogeneous material which does 
not become very readily stained. In this are embedded some 
five or six nuclei, one (or two) of which are larger than the others 
(about 0-008 to 0-01 mm. in long diameter), and are situated 
usually about the middle of the length of the fibre, while the 
rest are mostly towards the outer end. ‘The core has a thin 
investinent of what looks like fibrillated material. 
