41 



filled by a peculiar substance wliOLje nature I liave not 

 been able to determine. In living specimens tlie mantle is 

 of a light grayish, translucent appearance. But specimens 

 in alcohol become of almost a chalky whiteness, due to tha 

 masses of this peculiar material. Each lacunar space is 

 filled by a more or less spherical nodule, which is just 

 visible to the naked eye. Examined by transmitted light, 

 these nodules are very opaque and seem composed of granu- 

 lar particles; by reflected light they are white. They 

 are insoluble in acids, but soluble in water and quickly 

 disappear in aqueous solutions. Deshayes described them 

 as non-nucleated mucous cells. They are apparently the 

 "siliceous particles" which Hancock observed, and with 

 which he supposed the burrow to be formed. They are not 

 cells, but deposits of some sort. It seems that they 

 ahould be regarded as constituting a reserve of mucilagi- 

 nous material of some sort for use as occasion may require. 



Special Gland of tlie Mantle. - Lying between the two ep- 

 idermal layers of the mantle, in the mid-dorsal region 

 near the extreme posterior end of the body, there is a 

 small special gland which is peculiar to the "Ship-wormn !• . 



