362 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
The muscle is well supplied with blood brought by 
the adductor artery, and the whole substance of the muscle 
is permeated with lacunar spaces in which blood cor- 
puscles can be seen. The adductor contains also a very 
large quantity of glycogen, which can be easily extracted 
with water and the characteristic tests applied to the 
solution. The means of attachment of the adductor 
muscles to the valves can be best observed in complete 
sections through a very small Pecten, the shell of which 
has been decalcified. The union of the muscle fibres with 
the shell is carried out by a special attachment epithelium, 
the cells of which fuse with the muscle fibres so that their 
original epithelial nature is difficult to trace; and this 
tissue element appears to secrete the specialised layer of 
shell at the adductor impressions (fig. 2, Sh. m.). 
The Radial Pallial Muscles (figs. 1, 3 and 4, Pall. 
VU. 7.) are confined to the edges of the mantle lobes, and 
their attachments and course as seen in surface view, 
have been described above. At the point where they are 
attached to the shell, the epithelial cells can be seen 
extending between them and the shell, but slightly 
modified. From this point, where the fibres are inserted 
very obliquely, they pass outwards, towards the margin 
of the mantle lobes, drawing gradually nearer to the inner 
surface of the mantle, until most of them terminate at the 
base of the velum. In certain sections taken through the 
mantle of P. opercularis, some of these fibres appear to be 
striated, the stripes being apparently transverse. The 
striping, however, is not nearly so obvious nor so regular 
as that of the adductor muscle, and, moreover, it cannot 
be seen in all sections, even those cut very near to each 
other and treated with the same fixative and stains. The 
question arises, therefore, whether this cross striation 
seen in some of the radial pallial muscles is not due to the 
