excurrent orifice side by side at the outer end, the reproductive organs develop, and a purely vegetative existence within such protection as is given by a leathery, contractile tunic, takes the place of the promising condition of early youth. There is, however, a minute animal swimming about on the surface of the sea, named Appen- dicularia, which seems to belong here, and is like an ascidian larva, which preserves its chord- ate condition throughout life.
These simple, solitary ascidians are bi-sexual, and increase only by spawning: but the composite tunicates form colonies by budding, as well as emit eggs, and the economy of some of these communities is very complicated. See Balanoglossus; Chordata: and articles under Alimentary System, Evolution of; Nervous System, Evolution of; and similar titles, for Comparative Anatomv and relationships of the class. Consult Parker and Haswell, Text-Book of Zoölogy (New York, 1898).
Explanation of Plate of AScidians, etc.
1. A SIMPLE ASCIDIAN: a, mouth: b, exhalent pore. 2. A CREEPING FORM (Clavellina), showing stolons. 3. SAME AS No. 2: a, mouth: 6. branchiæ: c, nervous centre; d, stomach; e, genital gland; f, exhalent pore; g, anus; h, stolons. 4. PORTION OF BRANCHIÆ, enlarged. 5. AN ENCRUSTING COMPOUND .ACIDIAN (Botrylloides). 6. DIAGRAM OF PART OF 5, showing structure: the arrows indicate inward and outward water currents. 7. COLONY OF FREE LUMINOUS ASCIDIANS (Pyrosoma). 8. ASCIDIAN EMBRYOS (tadpole stage), showing changes of form with growth, and disappearance of notochord (noto): a, youngest full-swimming tailed stage; b, larva recently fixed; c, older fixed stage; d, section of tail of a, showing relation of fins to notochord. 9. BALANOGLOSSUS; br, branchial region; co, collar; gen, genital ridges; hep, prominences formed by he- patic cæca: pr, proboscis. 10. Enlarged section of upper part of 9: prob. proboscis; div, supposed notochord (diverticulum); mo, mouth; dors, dorsal-vessel.
ASCLE'PIADA'CEÆ (named after Ascle-
pias). The milkweed family. A natural or-
der of dicotyledonous plants, the members of
which are herbs or shrubs, often with twining
stems, and mostly with a milky juice. The
leaves are entire and without stipules. The
flowers, which are commonly produced in umbels,
are peculiar in structure, but perfectly sym-
metrical and regular. The calyx is small or
none; corolla five-parted, the lobes often re-
flexed; a crown of five-hooded bodies is seated
upon the tubes of the stamens, each containing
a curved horn: stamens five, inserted upon the
corolla; pollen grains coherent into two or four
waxy masses, somewhat as in some orchids;
ovary of two carpels, styles short and united by
their disk-shaped stigma. Fruit of two follicles
or pods; seed usually flattened and provided
with long, fine hairs; embryo about as long as
the seed; cotyledons flat.
This order, which is closely related to Apo- cynaceæ, embraces more than 200 genera, and nearly 2000 species, which are widely distributed throughout the warmer portions of the globe, being especially numerous in Africa. The prin- cipal representative of the order in the United States is the well-known Asclepias (q.v.), or milkweed. The main sections of the order are Periplochæ represented by the genera Peri- ploca and Streptocaulon; Asclepiadeæ, which includes Asclepias and Cynanchum, including
Vincetoxicum; Tylophoreæ, of which the chief genera are Marsdenia, Stephanotis, Cereopegia, Stapelia, and Hoya; and Gonolobeæ, represented by Gonolobus. The plants of this order vary widely in their characteristics and uses. Many are cultivated for their delightful perfume, as Stephanotis floribunda, etc., while others, such as some species of Stapelia and Hoya, are known as carrion-flowers, from their repellent odor. Flies are attracted by them, and eggs are often deposited upon the flowers. Some species of Asclepias yield fibre from their stems, and the silky fibre of their pods has many uses. Others yield valuable fibre. Among them are species of Marsdenia, Periploca, and Orthanthera. For the economic uses of others see Indian Sarsaparilla; Mudar; Argel; Cynanchum.
AS'CLEPI'ADÆ (Gk. 'AaK/.y-iaSat, Asklēpiadai).
Originally an association, claiming descent from the god of healing, Asclepius, or Æsculapius (q.v.), in which the practice of medicine was hereditary. Later those not connected by blood were admitted, and the organization, which existed in various parts of Greece, became a training-school for physicians. After the time of Hippocrates, the Asclepiadæ seem to have required a comprehensive course of study of their candidates, and the so-called Hippocratic Oath shows the ethical standard they maintained.
ASCLEPIADES, as'kle-pi'a-dez (Gk, 'ActicXt?-
-ia67/c, Asklēpiadēs. A Greek physician, born at
Prusa or Cius, in Bithynia. He lived at the be-
ginning of the First Century B.C. He was at
first a teacher of oratory at Rome, but later,
without any previous preparation therefor,
turned to the practice of medicine. What As-
clepiades lacked in real knowledge, he supplied
by clear-sightedness and understanding of human
nature. He aimed to effect his cures by simple
and pleasant remedies. Thus, he made unlimited
use of wine, recommended frequent baths, diet-
ing, and exercise, while he denounced the exces-
sive use of emetics and purgatives. One of his
leading doctrines was, that all disease arose from
an inharmonious distribution of the small, form-
less corpuscles of which the body is composed.
He is said to have been the first to distinguish
between acute and chronic diseases, but his
knowledge of anatomy was apparently slight.
Seventeen treatises of Asclepiades are mentioned.
The fragments of his writings, which have been
preserved, were edited by Gumpert, Asclepiadis Bithyni Fragmenta (Weimar, 1798).
ASCLEPIADES of Samos. A Greek poet of the Second Century A.D., a younger contemporary of Theocritus. He was the author of thirty-nine epigrams, mostly erotic, in the Greek anthology. The Asclepiadean metre probably was named after him.
ASCLE'PIAS (so named from Asclepius, father of medicine), or Swallow Wort. A genus of the order Asclepiadaceæ, most of the species of which are natives of America, where they are commonly called milkweeds, on account of the milky exudation that occurs at any part cut or injured. The numerous seeds contained in the pods are copiously covered with down, and are dispersed by the wind. The milky juice of some species is said to contain caoutchouc, or a substance resembling it. The corolla is wheel-shaped, and reflexed with a corona of variously
