252 
THE CABINET OF NATURAL HISTORY 
that the animal economy of these two molluscae is singularly 
adapted to their mutual benefit; the velella supplying nour- 
ishment and a floating apparatus to the ianthina, and the 
ianthina, by its attachment below so balancing and ballasting 
the velellse, as to preserve it in an upright position, which 
is necessary to its motions through the water. However 
this may be, there appeared, upon closely examining a 
great number, but little injury sustained by the velellae from 
its parasite. Some of the adhering shells were quite young, 
and others full grown specimens. As far as my knowledge 
in natural history extends, the ianthina was never before 
ascertained to be parastitic to the velella, or made use of 
its buoyancy on the surface of the waves to supply the place 
of its own beautiful apparatus of air cells. This fact con- 
firms the acuteness of Cuvier, that accurate observer of na- 
ture, who justly concluded that the ordinary floating appa- 
ratus of the ianthina was sometimes naturally absent; as, in 
some specimens of the animal which he examined, not a 
vestige of that organ could be perceived, and no scar or cica- 
trix on the foot, by which it is secreted, could, on the most 
minute examination, be discovered. 
Both the ianthina and velella seem to throw out a violet 
coloured liquid, when first captured. The purple fluid dis- 
charged by these animals will stain a w r hite handkerchief a 
fine rich colour. As the ianthina is often found in the 
Mediterranean sea, it has been suggested, with some plau- 
sibility, that this purple fluid may be the basis of the Tyrian 
dye, or ancient royal purple, accidentally discovered by the 
dog of Hercules. I regret very much that I could not try 
the effect of acids and alkalies on this colour. According 
to Pliny, alkalies gave it a green tint; if so, it is analogous 
to a vegetable blue or purple. We are informed by Stavo- 
rinus, that when the liquid obtained from the ianthina is 
evaporated to dryness, a powder is obtained, which, on 
being mixed with gum-water, forms a beautiful purple paint. 
Since writing the above, I find, in a late foreign journal, 
that Mr. Lesson has satisfactorily proved that the Tyrian 
purple, noticed by Pliny, was undoubtedly derived from 
the ianthina. He states, from some imperfect trials, that 
the colour of the ianthina will form a valuable re-agent, for 
it passes very readily to red, under the action of acids, and 
returns to blue under that of alkalies. With the oxalate of 
ammonia it gives a precipitate of a dark blue colour, and 
with the nitrate of silver a very pleasant greyish blue, both 
of which are good colours for drawing. 
I am doubtful as to the specific name both of the ianthina 
and velella above noticed. The velella approaches very 
near to the V. mutica, but the tentaculse on the under sur- 
face cover it completely, except a narrow space at the mar- 
gin, and a small portion immediately round the mouth; 
they are also longer near the margin, and gradually dimin- 
ish in length as they recede inwards. If the animal proves 
to be new, I shall call it Velella atlantica. 
The ianthina is very closely allied to the I. globosa 
figured in Swainson’s Zoological Illustrations, though the 
shell is by no means so large and beautifully coloured as 
those there represented. 
SUMMER DUCK, OR WOOD DUCK. 
[Plate XXII.] 
Le Canard d’Etb, Briss. vi. p. 351. 11 . pi. 32. fig. 2 . — 
Le beau Canard huppb, Burr, xx, p. 245.— PI. Enl. 
980. 981. — Summer Duck, Catesby, i , pi. 97. — Edw. 
pi. 101. — Jlrct. Zool. No. 943. — Lath. Syn. in. p. 
546.— -Anas sponsa, Gmel. Syst. i, p. 539, No. 43. — 
Ind. Orn. p. 876, No. 97. — Philadelphia Museum. 
“This most beautiful of all our Ducks, has probably no 
superior among its whole tribe for richness and variety of 
colours. It is called the Tv%od Duck, from the circum- 
stance of its breeding in hollow trees ; and the Summer 
Duck, from remaining with us chiefly during the summer. 
It is familiarly known in every quarter of the United States, 
from Florida to Lake Ontario, in the neighbourhood of 
which latter place I have myself met with it in October. 
It rarely visits the seashore, or salt marshes; its favourite 
haunts being the solitary deep and muddy creeks, ponds, 
and mill dams of the interior, making its nest frequently in 
old hollow trees that overhang the water. 
The Summer Duck is equally well known in Mexico and 
many of the West India islands. During the whole of our 
winters they are occasionally seen in the States south of the 
Potomac. On the tenth of January I met w r ith two on a 
creek near Petersburg in Virginia. In the more northern 
districts, however, they are migratory. In Pennsylvania 
the female usually begins to lay late in April or early in 
May. Instances have been known where the nest was con- 
structed of a few sticks laid in a fork of the branches; usu- 
ally, however, the inside of a hollow tree is selected for 
this purpose. On the eighteenth of May I visited a tree 
containing the nest of a Summer Duck, on the banks of 
Tuckahoe river, New Jersey. It was an old grotesque 
white oak, whose top had been torn off by a storm. It 
stood on the declivity of the bank, about twenty yards from 
the water. In this hollow and broken top, and about six 
feet down, on the soft decayed wood, lay thirteen eggs, 
snugly covered with down, doubtless taken from the breast 
of the bird. These eggs were of an exact oval shape, less 
