8 
PROFESSOR H. N. MOSELEY. 
offsets enter thè canal plexus by two sets of openings ; fìrstly, 
at thè margins of thè tegmenta, which adjoin thè borders of thè 
girdle by a series of fine apertures in thè shell substance, 
which occupy narrow band-like areas intervening between thè 
tegmenta and upper surfaces of thè articulamenta at their lines 
of junction with one another. These bands are sieve-like in 
appearance, being perforated all over, and lie just beneath thè 
external margin of thè tegmenta. Secondly, oflfsets of thè 
mantle tissue enter thè canal plexus at thè incisurse, and by 
means of fine pore-like apertures on thè under surfaces of thè 
shells. These pores may be irregularly scattered, as, e. g. in 
thè case of thè anterior and posterior shells of Corephium 
aculeatum, or they may be concentrated along thè so-called 
suturai lines of thè shells which spi’ing from thè marginai 
notches or incisurae. The suturai lines where present in thè 
anterior and posterior shells radiate from thè apices (or 
mucrones) of thè shells to thè marginai notches. There are 
six such radiating suturai lines in thè anterior shell of Schi- 
zoehiton, and six corresponding notches (see PI. IV, fig. 5.) 
On each median shell there are a single pair of faterai suturai 
lines, and a corresponding single pair of notches. The suturai 
lines are marked on thè under surfaces of thè shells by a series 
of small slit-like apertures, directed transversely to thè lengths 
of thè lines, and when thè shell is removed from its bed corre- 
sponding minute transverse processes of thè mantle are seen 
projeeting along corresponding lines on its surface, and torn 
across. Processes of thè mantle tissues also enter thè shell 
canals at thè bottom of each marginai notch, and from thè 
notch longitudinal canals run in thè shell substance along thè 
suturai lines above thè series of slit-like apertures. 
The strings of soft tissue forming thè horizontal plexus show 
a finely fibrous structure, and contai n numerous nuclei and 
fine granular matter. They are not canals as believed by 
Marshall. They contain nerve-fibres within them, as is 
certain from thè fact that some of them expand into retinas ot 
typical structure in thè eyes. I bave been unable to trace thè 
nerves supplying thè soft tissue ramiti cations of thè tegmenta 
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