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BULLETIN OE THE BUREAU OF FISHERIES. 
tube (a, fig. 6) which opens into the pericardium; second, a short tube ( b ) which opens 
to the exterior; third, a central pouch (c) into which the tubes a and b open at their inner 
ends. This central pouch is large and irregular in shape. One branch of it extends 
upward over the posterior retractor of the foot and ends beneath the pericardium. (Tig. 
6, e.) This portion of the kidney is probably homologous with a kidney-like organ 
which Grobben (5) found in a number of lamellibranchs extending as a fold into the peri- 
cardium and connected below with a large sinus, which he believed to belong to the 
kidney. In Atrina it is plainly a branch of the main kidney. 
The glandular portion (fig. 6, h) is located at the posterior and outer end of the main 
pouch. It is quite extensive and is colored dark brown on account of the reddish brown 
excretory material which is inclosed by its cells. All other parts of the kidney appear 
colorless and thin walled. 
Fig. 6. — Drawing of the kidney in position, showing three well-marked parts, a tube (a) opening into the 
pericardium, a tube (6) opening to the exterior, and a large central pouch ( c ) into which tubes a and b 
open at their inner ends; e represents a prolongation of pouch c which extends upward beneath the peri- 
cardium; g, the genital duct; k , the glandular portion of the kidney; p, the pericardium. 
It will be noticed that this kidney differs considerably from the usual type, which 
is typically a coiled tube. In the form under consideration it may once have been a 
true coiled pouch. Its transformation may have come about by the fusion of the two 
branches of the central loop to form the single large pouch. 
While working with living specimens I frequently saw quantities of vellowish-brown 
material expelled from the kidneys. When examined under the miscroscope this 
material proved to consist of very numerous vacuolated cell-like bodies, which were 
filled with yellowish-brown or reddish-brown globules of excretory matter. Each 
excreted body had a tuft of extremely long cilia which were still active. (Fig. 7.) After 
collecting and fixing some of this excreted matter I stained it with iron-alum hsema- 
toxylin to see if there were nuclei present. None were found and I believe that none 
are thrown off. Paraffin sections of the glandular portions of the kidney show the 
epithelial cells to be greatly vacuolated and filled with this excretory matter. (Fig. 8.) 
The vacuole is located in the outer end of the cell and there is very little protoplasm 
