commenced in one spot,
apparently on the surface of one of the zooeids, and gradually
spread from this as a centre in all directions; then the whole
was lighted up: it remained brilliant for a few seconds, and then
gradually faded and died away, until the whole mass was dark
again. Friction at any point induces the light at that point, and
from thence the phosphorescence spreads over the whole, while the
creature is quite freshly taken; afterwards, the illumination
arising from friction is only local."

Dealing with these creatures in the broad anatomical spirit with which
he had studied the Medusae, Huxley shewed the typical structure
manifested in the different forms, and that was common to them and the
Ascidians or sea-squirts of the seashore. In a second paper on
"Appendicularia and Doliolum" he made further contributions to our
knowledge of these interesting creatures. Appendicularia is a curious
little Ascidian, differing from all the others in its possession of a
tail. Earlier observers had obtained it on various parts of the ocean
surface, but had failed entirely to detect its relationship to the
ordinary Ascidians. Chamisso got it near Behring's Straits and thought
that it was more nearly allied to "Venus's Girdle," a Coelenterate.
Mertens, another distinguished zooelogist, had declared that "the
relation of this animal with the Pteropods (a peculiar group of
molluscs) is unmistakable"; while Mueller, a prince among German
anatomists, confessed that "he did not know in what division of the
animal kingdom to place this creature." Huxley shewed that it
possessed all the characteristic features of the Ascidians, the same
arrangement of organs, the same kind of nervous system, a respiratory
chamber formed from the fore part of the alimentary canal, and a
peculiar organ running along the pharynx which Huxley called the
endostyle and which is one of the most striking peculiarities of the
whole group. The real nature of the tail was Huxley's most striking
discovery. He pointed out that ordinary Ascidians begin life as tiny
tadpole-like creatures which swim freely by the aid of a long caudal
appendage; and that while these better-known Ascidians lose their
tails when they settle down into adult life, the Appendiculariae are
Ascidians which retain this larval structure throughout life. Von Baer
had shown that in the great natural groups of higher animals some
forms occur which t