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form with great rapidity an enormously large investing gelatinous layer (fig. II), which corresponds to the test of other groups. This was first described by von Mertens and by him named " Haus." It is only loosely attached to the body and is frequently thrown off soon after its formation and again reformed.

H. I.ohmann has made a careful study of the mode of formation of this " house " from certain large ectoderm cells, the " oikoplasts," and he considers that it probably fulfils the following functions: Its complicated apparatus of passages with partial septa form a finely perforated network, through which a relatively large See also:

VOLUME

volume of See also:

WATER

water is strained so as to entrap microscopic See also:

food particles; it See also:

HELPS, SIR ARTHUR (1813-1875)

helps in locomotion by its hydrostatic effect, and it is also a See also:

PROTECTION

protection to the See also:

animal, which may See also:

ESCAPE (in mid. Eng. eschape or escape, from the O. Fr. eschapper, modern echapper, and escaper, low Lat. escapium, from ex, out of, and cappa, cape, cloak; cf. for the sense development the Gr. iichueoOat, literally to put off one's clothes, hence to sli

escape from enemies by throwing off the house, which is many times its own See also:

SIZE

size. The tail in the Appendiculariidae is attached to the ventral surface of the body (fig. 18), and usually points more or less anteriorly. The supposed traces of vertebration in the muscle bands and the nerve cord are probably artifacts, and do not indicate true metameric segmentation. Near the See also:

BASE

base of the tail there is a distinct elongated ganglion (fig. 18, ng'). The anterior (cerebral) ganglion has connected with it an otocyst, a pigment spot, and a tubular See also:

PROCESS

process opening into the branchial sac and representing the dorsal tubercle and associated parts of an See also:

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary Ascidian. The branchial See also:

APERTURE (from Lat. aperire, to open)

aperture or mouth leads into the branchial sac or pharynx. There are no tentacles. The endostyle is See also:

SHORT, FRANCIS JOB (1857– )

short. There is no dorsal lamina, and the peripharyngeal bands run dorsally and posteriorly.

The See also:

wall of the branchial sac has only two ciliated apertures (fig. 19). They are homologous with the See also:

PRIMARY

primary stigmata of the typical Ascidians and the gill clefts of vertebrates. They are placed (From The Cambridge Natural History, vol. vii.," Fishes," &c. By permission of Macmillan & Co., Ltd.) (After Fol.) x, Lateral reticulated parts of " House." far back on the ventral surface, one on each side of the See also:

MIDDLE

middle See also:

LINE

line, and See also:

lead into short See also:

FUNNEL (through an O. Fr. founil, found in Breton, from Lat. infundibulum, that through which anything is poured, from fundere, to pour)

funnel-shaped tubes which open on the surface of the body behind the anus (fig. 18, at). These tubes correspond to the right and left atrial involutions Ovary. Peripharyngeal See also:

BAND

band. Cerebral ganglion. Caudal ganglion. Enlargement of nerve cord in tail. Sense-See also:

ORGAN

organ (tactile) on See also:

LOWER

lower See also:

LIP (a word common in various forms, to Teutonic languages, cf Ger. Lippe, Dan. laebe; Lat. labium is cognate)

lip.

Ciliated aperture in pharynx. See also:

STOMACH (Gr. vrbsaxos from arbga, a mouth)

Stomach. Testis. Urochord. Its cut end. which, in an ordinary Ascidian, fuse to form the peribranchial cavity. The See also:

heart, according to Lankester, is formed of two cells, which are placed at the opposite ends and connected by delicate contractile protoplasmic fibrils. The large ovary and testis are placed at the posterior end of the body. The See also:

REMAINDER, REVERSION

remainder of the structural details can be made out from See also:

FIGS

figs. 18 and 19. At, Atrial passage. n, Nerve. b.s, See also:

BLOOD

Blood sinus. n.ch, Notochord.

br.s, Branchial sac (pharynx). R, Rectum. ec, Ectoderm. sg, Stigma. en, Endoderm. t, Test. The family Appendiculariidae comprises amongst others the following genera: Oikopleura (Mertens), and Appendicularia (Cham.), in both of which the body is short and compact and the tail relatively long, while the endostyle is straight; Megalocercus (Chun) containing M. abyssorum, a huge deep-sea form from the Mediterranean (30 mm. long); Fritillaria (Quoy and Gaimard), in which the body is long and composed of anterior and posterior regions, the tail relatively short, the endostyle recurved, and an ectodermal See also:

hood is formed over the front of the bod ; and Kowalevskia (Fol), a remarkable form described by Fol body; in which the heart and endostyle are said to be absent, while the branchial sac is provided with four rows of ciliated tooth-like processes.

End of Article: CLASSIFICATION AND CHARACTERS OF

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