NATURAL HISTORY OF THE SHIP-WORMS. 229 
Fie. 17. Left shell valve of large adult. The lines of growth are shown natural size and relations, but 
the teeth are omitted. ™ 10. 
Fia. 18. Front view of shell of adult.» 7. 
Fic. 19. Internal view of right valve, apo, apophysis; aa and ap, attachment of anterior and posterior 
adductor muscles. 7. 
Fie. 20. Left pallet of specimen 5 mm. long. 70. 
PLATE XII. 
Fic. 21. Dorsal gland of the posterior part of the mantle. Section of whole gland of specimen 5 mm, 
long. The letters are placed in the epibranchial cavity; fol are secretory follicles; du, duct. 
x 700. 
Fig. 22. Sagittal section of a newly attached larva. The very large glands of the foot occupy a large 
part of the mass of the latter. A large quantity of material derived from these glands lies 
adjacent to the byssus gland. The disintegrating cells of velum, some of which have been 
eaten, are not represented. > 540. 
PLATE XIII. 
Fie. 23. Transverse section of larva. From a specimen in which the foot was more protracted than 
shown in figure 22. The ventral mantle edge is filled with cells gorged with material, evi- 
dently for the rapid growth of the shell during its transformation. 440. 
Fig. 24. Horizontal section of newly attached larva in which the cavity of the velum was partially 
obliterated. On the left side the contents of the gland of Deshayes are shown; on the right 
side, the duct. 440. 
PLATE XIV. 
Fic. 25. Transverse section of a specimen 1 mm. long, to show especially the extent and relations of 
the gland of Deshayes. 125. 
[Norr.—Figs. 26-33 are a series of transverse sections of a specimen 10 cm. long, along the lines 
indicated in figure 6. The drawings were made with the aid of a camera and afterwards 
touched up, though not essentially changed. The details of structure are semidiagrammatic. 
The right side in the sections is on the left side of the observer. All X 15.] 
Fic. 26. Section through the posterior adductor muscle and cephalic hood. Tubular part of style 
sheath to the right side. Posterior aorta asymmetrical, on the right side. 
Fic. 27. Section through the wound typhosole, the canal-like anterior end of the pericardial cavity 
and the posterior end of the body of the kidney. 
Fic. 28. Section through the large posterior liver mass. Shows the distribution and character of the 
two different parts of the liver. 
Fig. 29. Section through the large ventricle and the ovary. 
Fre. 30. Section through the opening of the kidney into the pericardial cavity, the anterior ganglion, 
and the posterior ends of the auricles. The two arrows from the right indicate the course 
of the water currents between the gill laminee, the one pointed dorsally, that of blood through 
the gill lamina. The number and distribution of the interlaminar connections indicated by 
dots. 
PLATE XV. 
Fic. 31. Section near the posterior end of the visceral mass. 
Fria. 32. Section to illustrate the structure in the long region between the visceral mass and the mus- 
cular collar. In this figure, but not in the other transverse sections, the corpuscles of the 
blood are represented in the blood vessels. 
Fic. 33. Section through the ‘‘collar,’’ pallet handles, and base of siphons. 
Fra. 34. Section of a pallet handle and its sheath. The attachment of the ventral retractor muscle is 
shown. X 272. 
Fries. 35, 36. Diagrams of the posterior end of body of adult, left side, to show the arrangement of the 
siphons and pallets and their muscles. In figure 35 the siphons are represented as extended, 
the pallets as retracted; in figure 36 the siphons are represented as contracted, the pallets 
as protracted. Ca, calcareous lining of burrow. 
