122 MusEuM AND Art NOoTES

When mature, ova are shed from the manubrium which hatch into small ovoid
bodies swimming freely by means of vibratory cilia (hairs) ; these are called planulae ;
after a short time they attach themselves to some solid body and develop into colonial
hydroids (one individual is shown in fig. 4), and the cycle may commence anew.

DESCRIPTION OF OIKOPLEURA.—This genus belongs to the Phylum Chordata, class
Tunicata order Larvacea, family Appendiculariidae; this family includes some eight
genera of which species of the genera Oikopleura, Appendicularia and Fritillaria are
not uncommon in the neritic plankton.

Otkopleura is a small tadpole-like animal with a “tail” attached to the body por-
tion; a notochord runs down the middle of the tail with nerve ganglions at intervals;
it is the first appearance of a notochord (spinal chord) in the ascending scale of
animal life, and, in consequence, the Tunicata are included in the great phylum
Chordata or vertebrate animals. |

In the other orders of Tunicata this notochord is present only during the
larval stages.

The body of Oikopleura contains reproductive organs; spermatozoa and ova being
shed at different periods; the ova hatch into larvae similar to that shown in fig. 6.

Among many other Tunicata may be mentioned the Ascidians (sea-squirts), the
compound Ascidians (Botryllus, etc.), both sedentary forms, the pelagic (plankton)
Salps and the luminescent species of Pyrosoma.