JAN. — MAR 1857.] voyage from England to Madras. 157 
not again resume their natural form. Fig. 28 which is placed here 
for the sake of comparison, is copied by permission of the 
Honorable Walter Elliot from his valuable collection of color- 
ed drawings of Nudibranch Molluscs. Mr. Elliot has sug- 
gested to me that my specimen may have lost all the digitated ap- 
pendages and this seems probable, for the animal in question, 
though it lived several days in a vessel of water, (thereby proving 
that the supposed missing organs were not branchioe) yet it showed 
no power of swimming or even of meving, beyond curving its body 
into various contortions when touched. It appears that the species 
of Glaucus are not as yet w^U determined, which may account for 
the apparently contradict »ry statements as to their habits, kc. One 
author affirms that the Glaucus " swims with great quickness," 
others describe it as being remarkably torpid and sluggish in its 
movements. Glaucus, Fig. 28, which was taken by Mr. Elliot, 
in the bay of Bengal near Vizagapatam, at no great distance from 
the shore,*" differs from my specimen not only in the number of 
the lateral appendages, but in the form and disposition of the blue 
lines on its surface. Both species are remarkable for the brilliancy 
of their color, which is generally attributed to their feeding on the 
beautiful blue Velellas and Porpitas, animals very low in the scale 
of animate objects, which are met with abundantly in these seas. 
This conclusion appears to me illogical. Most of the Pelagic animals 
we met with, were remarkably devoid of color, and such as had any 
were generally blue. Indeed with the exception of an occasional 
tinge of purple, I do not remember that we met with them of any 
other tint ; so that I think we must look elsewhere for the cause of 
this color prevailing so remarkably in Pelagic and other marine 
animals. It seems to me not improbable that Iodine,a powerful color- 
ing agent, universally prevalent in sea water, may be partly instru- 
mental in producing it. 
May 21st, Lat. 40-51 S. Long. 24-57 E. After dark we 
took in the net myriads of minute Ckijstacea not much 
^arger than cheese mites, of a pale blue color, and in the dark 
* The perfect specimens of this Glaucus when first captured moved with consi- 
derable rapidity. The branched appendages appeared to be very brittle and were 
easily brokea when attempting to catch the animal— W. E. 
