NATURAL HISTORY OF THE SHIP-WORMS, 225 
SUMMARY. 
The results of my work on ship-worms may be summarized as follows: 
(1) The larva is a typical free-swimming marine lamellibranch larva. 
(2) The whole velum is suddenly cast off and eaten, soon after the attachment of 
the larva. After the loss of the velum the young ship-worm is, in its general organi- 
zation, essentially a typical small bivalve. 
(3) The loss of the velum in ship-worms and in Ostrea (which I have also 
observed) indicates that the formation of the palps in lamellibranchs has no con- 
nection with the velum. 
(4) A byssus apparatus is present in the newly attached larva, but is functional 
for only a few hours. 
(5) The position and relations of the sheath of the crystalline style in thelarva 
indicate that this structure, in the more highly specialized lamellibranchs, is homol- 
ogous with the posterior half of the stomach of forms like Yoldia and Nucula. 
(6) The pleural ganglion of the larva is separate from the cerebral. 
(7) The transformation of the larva into the small ship-worm is so rapid as to 
amount to a metamorphosis. Almost the whole organization is involved —shell, 
mantle, foot, alimentary canal. 
(8) The posterior adductor muscle is the effective agent in forming the burrow, 
and the shell is the tool with which it works. 
(9) Inthe ship-worms there is a peculiar gland of unknown function in the mantle 
of the posterior part of the body. 
(10) A system of highly specialized muscles manipulate the pallets and are 
peculiar to ship-worms. 
(11) There is on either side but a half ctenidium. The anterior eleven gill fila- 
ments form small ‘‘plications”’ on the side of the ‘‘head,’’ separated by a wide space 
from the rest of the gill. 
(12) In close association with the gills is a prominent glandular structure of 
unknown function, which I have called the ‘‘gland of Deshayes.”’ It consists of two 
types of elements of remarkable character. 
(13) Through the elongation of the visceral mass, the positions of the two aorte 
have been reversed; i. e., the apparent posterior aorta is the real anterior and the 
apparent anterior the real posterior. 
(14) The cecum of the stomach is very large and apparently an important 
absorbent organ. The blind end of the style sheath is tubular and of very different 
character from the outer part. In XYylotrya the typhlosole of the anterior part of the 
intestine is remarkably developed into a complicated in-rolled duplicature. 
(15) The nervous system of the adult contains the three pairs of ganglia, well 
developed, as in typical lamellibranchs. The pedal ganglia are fused together; the 
cerebral are separated from each other by a long commissure. The ‘‘anterior 
ganglion” is a small ganglion separated from the visceral ganglion, and nerves from 
it innervate the kidneys, the genital organs, and the osphradium in part. 
(16) On the genital duct isan organ of special sense of unknown function. The 
sensory cells of the osphradium lie beneath the surface epithelium, Their peripheral 
