96 HERBERT E. DURHAM. 
“‘ pigment-holding guanin”” amongst the Capitellide. Though 
he does not describe any actual transference of pigment by 
wander-cells, he notes that blood-corpuscles (Blutscheiben) 
containing pigment concretions may become surrounded and 
encapsuled by a layer of leucocytes (p. 752), and that certain 
peritoneal epithelium-cells ingest concretions, and are to be 
considered phagocytic (pp. 753, 754) ; the figure 15 on pl. xxxv 
especially is suggestive of a transportation of concretions by 
wander-cells to different regions, e. g. skin, gut-wall, &c.; and 
if further observation shows this to be the case EHisig’s conclu- 
sions on the specific excretory powers of such parts will require 
modification. 
Amongst the Mollusca we have some evidence that wander- 
cells may take part in the excretory process. First of all the 
well-known observation that cells loaded with uratic concre- 
tions actually break off from the renal epithelium is not without 
interest in this connection (vide, e.g., Vogt and Jung, No. 6, 
p- 811). 
Grobben (No. 33) has shown that the part played by the 
cells of the pericardial gland in Lamellibranchs is in more 
perfect parallel with the process we are considering. He 
describes how cells laden with pigment concretions are liberated 
from the pericardial giand and pass into the nephridium from 
the pericardium, and so gain the exterior. It seems possible 
that some of the cells described formerly as being free renal 
epithelium-cells may be really of this nature, but it is not 
necessary to press this further here. 
I have made some preliminary investigations on the siphonal 
portion of the mantle in specimens of Anodonta and Unio; 
this region is black in colour as seen by the naked eye. In 
sections (vide figs. 6 and 7) the epithelial cells are seen to 
contain numerous small dark pigment-granules, which are 
located for the most part external to the nuclei. Here and 
there pigment is also present in the basal parts of the cells, 
and strands consisting of rows of pigment-granules may some- 
times be seen running up through the basement layer to the 
bases of the epithelium-cells. In the tissue below the epi- 
