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The uiuscle is well supplied with l)]oncl biouo-lit hy 

 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 Pecteu, 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. 

 M . /'.) 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. oijercularis, 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 muscdes is not due to the 



