224 BULLETIN OF THE BUREAU OF FISHERIES. 
to the end of the afferent duct. Then it passes ventrally and posteriorly (fig. 61, 62, 
66) to open near the midline into the epibranchial cavity, under the visceral ganglion. 
The efferent duct is lined with columnar, vacuolated and apparently secretory cells, 
which are not ciliated except at the anterior end and near the external opening. 
Venous blood from the posterior end of the body returns by the afferent renal 
vein (fig. 31, 32, ar v) which runs in the mantle, and on a level with the posterior 
ends of the duct, enters the peri-renal blood spaces (fig. 27-29, 31). After bathing 
the kidneys, it enters the general venous circulation. 
Pelseneer, who, it seems, observed only the posterior ends of the kidney duct, 
described them as much pouched. In properly prepared specimens of X. gouldi‘ 
I find that, while the body of the kidney is much pouched, the ducts form straight 
cylindrical tubes. Preserved ship-worms are almost always very greatly contracted 
and shrunken, and I am inclined to believe that this fact accounts for Pelseneer’s 
results. Also, contrary to the statements in text-books (Lang), I find that the two 
kidneys of Y. gouldi do not communicate with each other, as they do in Pholas and 
other forms. In the larva the kidneys lie anterior to the posterior adductor muscle 
and lateral to the visceral ganglion (fig. 7, 24, 26). As the visceral ganglion passes 
under and posterior to the muscle, the kidneys accompany it (fig. 9). In the early 
stages each kidney consists of a simple loop (fig. 9), of which the branch opening to 
the exterior seems to be excretory. As the ship-worm elongates, the chief secretory 
portion of the kidney remains with the muscle, while the two ducts become very 
long and their openings accompany the visceral ganglion. 
REPRODUCTIVE ORGANS. 
The first stage in which I have observed the reproductive organs is in speci- 
mens 2 mm. long, in which there is a mass of undifferentiated primordial germ 
cells under the visceral ganglion, As growth takes place processes grow out from 
the original organ till, in the adult, the sexual organs occupy a large part of the 
posterior portion of the visceral mass (fig. 10, 29-31). As the sexual products 
develop, they are stored in the cavities of the organ, and especially of that part first 
formed (fig. 63, 64, ov), which serves as a duct for the rest of the organ. The real 
sexual duct is remarkably short. It is formed as an ectodermal invagination which 
is already present in specimens 2 mm. long, but which does not break through into 
the sexual organ till sexual maturity. 
In the adult ship-worm the sexes are separate. Young specimens (14 cm. long) 
of X. gouldi, however, are very frequently hermaphrodite. As in all such cases the 
sperms are developed first, it appears that the species may be protandrous. In the 
adults I have observed no external differences between the sexes. In the male there 
is, however, a remarkable development of mucous gland cells on the dorsal side of 
the epibranchial cavity, while in the female they are not usually developed in this 
region, 
