214 THE ACEPHALA. $ 196. 
remains to notice a very remarkable organ found in all the Lamellibranchia, 
and known as the Gland of Bojanus. 
This organ, undoubtedly of a renal nature, is always double, and consists. 
of a large long sac with glandular walls, and of a dirty-yellow or dark- 
green color. It is situated each side of the back between the pericardium 
and the inferior adductor muscle, and extends usually upon the sides of 
the abdomen to the base of the branchiae. 
Quite often these glands are united upon the median line of the back -— 
their cavities being separated only by a thin septum. They communicate 
with the cavity of the mantle by two small openings which have swollen 
borders and are situated sometimes at the upper, and sometimes at the lower 
end of the sac. 
The usually very thin walls of these two sacs have numerous folds or 
plicae, which form compartments or areolae, all of which are covered with 
a very delicate ciliatel epithelium. The parenchyma of these walls is. 
composed of a very loose tissue, which, upon the least disturbance, sepa~ 
rates into small granular cells. Most of these cells contain a blue-black 
round nucleus, to which is due the more or less deep color of these 
organs. 
2With Unio, and Anodonta, these orifices are 
at the superior extremity of the renal sacs close 
beside the two genital openings; see Bojanus, Isis, 
1819, p. 46, Taf. I. fig. 1; Baer, in Muller’s Arch. 
1830, p. 319, Taf. VIT. fig. 1,2; Pfeiffer, Natur- 
gesch, deutsch. Land-und Susswasser-Mollusken, 
Abth. II. Taf. II. fig. 19, b.; and Neuwyler, in 
the Neue Denkschr. VI. p. 22, Taf. I. II. They 
lie in the angle formed by the abdomen and the in- 
ternal branchiae, and concealed beneath the inter- 
nal leaf of these last. They had already been ob- 
served by Poli (loc. cit. I. p. 6, Tab. IX. fig. 15, 
i.i.), who, however, did not recognize their true 
nature. 
With Pecten, and Spondylus, these renal sacs, 
which are situated in front of the adductor muscle, 
have their two orifices at the lower extremity ; see 
Garner, Trans. of the Zool. Soe. loc. cit. Pl. XIX. 
fig. 2, j. (Pecten). 
With many, the genital organs open into the 
urinary ones. This is so according to Garner (loc. 
cit. p. 92), with T'eddina, Cardium, Mactra, Pho- 
fas,and Mya. I have very distinctly seen with 
Pinna nobilis, the two orifices common to the kid- 
neys and genital organs. ‘heir borders were 
swollen, and they were situated upon the anterior 
surface of the dorsal walla little in front of the 
posterior adductor muscle. They opened into a 
very large sac with thin walls which had no gland- 
ular structure except at their lower extremity 
near the principal adductor muscle ; see Poli, loc. 
cit. Tab. XX XVII. fig. 2, D. 
The genital orifices open into the two sacs di- 
rectly back of these external orifices. With Myti- 
dus edulis, the kidneys have a yet more singular 
arrangement ; their two sacs situated at the base 
of the branchiae are open their whole length, so 
alone. This would seem inefficient did we not re- 
member their unceasing action ; and this view is 
the only one which will explain the exact conform- 
ation of the excavation to the shape of the body in 
allits parts. Itis the view of Agassiz, and others, 
who have specially examined the subject. I have 
here thus noticed the matter in a suggestive point of 
view for microscopical anatomists. — Ep. 
that by spreading apart the branchiae, the com- 
partments and cells of these glands can be distinct- 
ly seen ; see T'reviranus. Beobacht. aus d. Zool. u. 
Phys. p. 51, fig. 68, b.* 
8 Itis only recently that the intimate structure 
of these organs was known. .Veuwyler was quite 
mistaken in regarding them as two testicles (loc. 
cit. p. 25). He speaks of tubes in which he affirms 
that he has seen spermatic particles, but he gives 
neither a detailed description nor a figure.of one 
or the other. I have never been able to find 
anything of this kind in the Lamellibranchia. If 
the walis of these organs are prepared in any way 
for microscopic examination, a part of their paren- 
chyma tes into a vesi granular mass, 
the particles of which have a very lively dancing 
motion. The motions are due to portions of ciliated 
epithelium adhering to the cells and granules. It 
is in this way, probably, that Newwyler has been 
deceived, taking these moving bodies for spermatic 
particles, 
4 These round nuclei, usually of a deep brown or 
blue color, can easily be seen in the kidneys of 
Unio, Anodonta, and Cyclas ; but with the young 
individuals their number and size are quite limited, 
making the kidneys very pale. They resemble, 
moreover, perfectly the bodies contained in the 
renal substance of the Gasteropoda (see below). 
This analogy is particularly striking with Asper- 
gillum vaginiferum, whose renal sacs are tri- 
aggular and situated between the heart and the 
extremity of the rectum, thus resembling in all re- 
spects the kidneys of the Gasteropoda, although 
Leuckart has taken them for the liver (Neue. wir- 
bellose Thiere d. roth. Meeres, loc. cit, p. 46, Taf. 
XIL. fig. 6, g.). 
* [§ 196, note 2.] According to Frey and 
Leuckart, the bodies of Bojanus are absent in 
Teredo navalis, but these observers think the kid- 
neys are present in another part of the body ; see 
loc. cit. p. 46. — Ep. 
