Abdomen

(Lat. abdomen; from abdo, I conceal. Sometimes regarded as a contraction of adipomen, from adeps, fat.) The posterior cavity of the body, containing the intestines and others of the viscera.

Aberrant

(Lat. aberro, I wander away). Departing from the regular type.

Abiogenesis

(Gr. a, without; bios, life ; genesis, origin). Spontaneous generation, or the production of living beings without pre-existent life.

Abnormal

(Lat. ah, from ; norma, a rule). Irregular; deviating from the ordinary standard.

Abomasum

The fourth cavity of the complex stomach of the Ruminants.

Abranchiate

(Gr. a, without; bragchia, gills). Destitiite of gills or branchiae.

Acalephae

(Gr. akalephe, a nettle). Applied formerly to the Jelly-fishes or Sea-nettles, and other Radiate animals, in consequence of their power of stinging, derived from the presence of microscopic cells, called "thread-cells," in the integument.

Acanthocephala

(Gr. akantha, a thorn; kephale, head). A class of parasitic worms, in which the head is armed with spines.

Acanthometrina

(Gr. akantha ; and metra, the womb). A family of Protozoa, characterised by having radiating siliceous spines.

Acanthopterygii

(Gr. akantha, spine; pterux, wing). A group of bony fishes with spinous rays in the front part of the dorsal fin.

Acarina

(Gr. akari, a mite). A division of the Arachnida, of which the Cheese-mite is the type.

Acephalous

(Gr. a, without; kephale, head). Not possessing a distinct head.

Acetabula

(Lat. acetabulum, a cup). The suckers with which the cephalic processes of many Cephalopoda (Cuttle-fishes) are provided.

Acetabulum

The cup-shaped socket of the hip-joint in Vertebrata.

Acontia

(Gr. akontion, a javelin). Long filaments, charged with thread-cells, attached to the free edges of the mesenteries of Sea-anemones.

Acrita

(Gr. akritos, confused). A term sometimes employed as synonymous with Protozoa, or the lowest division of the animal kingdom.

Actinomeres

(Gr. aktin, a ray ; meros, a part). The lobes which are mapped out on the surface of the body of the Ctenophora, by the ctenophores, or comb-like rows of cilia.

Actinosoma

(Gr. aktin ; and soma, body). Employed to designate the entire body of any Actinozoon, whether this be simple (as in the Sea-anemones), or composed of several zooids (as in most Corals).

Actinotrocha

(Gr. aktin, ray; trochos, wheel). The form of Invertebrate larva seen in some of the Annelides, etc, in which there is a circlet of cilia round the anterior extremity.

Actinozoa

(Gr. aktin; and zoon, an animal). That division of the Coelen-terata of which the Sea-anemones may be taken as the type.

Adelarthrosomata

(Gr. adelos, hidden; arthros, joint; soma, body). An order of the Arachnida.