Part 621

Pro`to*ver"te*bra (?), n.; pl. ProtovertebrÊ . [Proto- + vertebra.] (Anat.) One of the primitive masses, or segments, into which the mesoblast of the vertebrate embryo breaks up on either side of the anterior part of the notochord; a mesoblastic, or protovertebral, somite. See Illust. of Ectoderm.

The protovertebrÊ were long regarded as rudiments of the permanent vertebrÊ, but they are now known to give rise to the dorsal muscles and other structures as well as the vertebral column. See Myotome.

Pro`to*ver"te*bral (?), a. (Anat.) Of or pertaining to the protovertebrÊ.

Pro*tox"ide (?), n. [Proto- + oxide: cf. F. protoxide.] (Chem.) That one of a series of oxides having the lowest proportion of oxygen. See Proto-, 2 (b).

protoxide of nitrogen, laughing gas, now called hyponitrous oxide. See under Laughing.

Pro*tox"i*dize (?), v. t. (Chem.) To combine with oxygen, as any elementary substance, in such proportion as to form a protoxide.

||Pro`to*zo"a (?), n. pl. [NL., fr. Gr. &?; first + &?; an animal.] ||(Zoˆl.) The lowest of the grand divisions of the animal kingdom.

The entire animal consists of a single cell which is variously modified; but in many species a number of these simple zooids are united together so as to form a compound body or organism, as in the Foraminifera and VorticellÊ. The reproduction takes place by fission, or by the breaking up of the contents of the body after encystment, each portion becoming a distinct animal, or in other ways, but never by true eggs. The principal divisions are Rhizopoda, GregarinÊ, and Infusoria. See also Foraminifera, Heliozoa, Protoplasta, Radiolaria, Flagellata, Ciliata.

Pro`to*zo"an (?), a. (Zoˆl.) Of or pertaining to the Protozoa. -- n. One of the Protozoa.

Pro`to*zo"ic (?), a. 1. (Zoˆl.) Of or pertaining to the Protozoa.

2. (Geol.) Containing remains of the earliest discovered life of the globe, which included mollusks, radiates and protozoans.

||Pro`to*zo"ˆn (-n), n.; pl. Protozoa (#). [NL.] (Zoˆl.) (a) One of the ||Protozoa. (b) A single zooid of a compound protozoan.

Pro`to*zo"ˆ*nite (?), n. (Zoˆl.) One of the primary, or first-formed, segments of an embryonic arthropod.

||Pro*tra`che*a"ta (?), n. pl. [NL. See Pro-, and Trachea.] (Zoˆl.) ||Same as Malacopoda.

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Pro*tract" (?), v. t. [imp. & p. p. Protracted; p. pr. vb. n. Protracting.] [L. protractus, p. p. of protrahere to forth, protract; pro forward + trahere to draw. See Portrait, Portray.] 1. To draw out or lengthen in time or (rarely) in space; to continue; to prolong; as, to protract an argument; to protract a war.

2. To put off to a distant time; to delay; to defer; as, to protract a decision or duty. Shak.

3. (Surv.) To draw to a scale; to lay down the lines and angles of, with scale and protractor; to plot.

4. (Zoˆl.) To extend; to protrude; as, the cat can protract its claws; -- opposed to retract.

Pro*tract", n. [L. protractus.] Tedious continuance or delay. [Obs.] Spenser.

Pro*tract`ed (?), a. Prolonged; continued.

Protracted meeting,a religious meeting continued for many successive days. [U. S.]

-- Pro*tract"ed*ly, adv. -- Pro*tract"ed*ness, n.

Pro*tract"er (?), n. A protractor.

Pro*tract"ile (?), a. Capable of being protracted, or protruded; protrusile.

Pro*trac"tion (?), n. [L. protractio.] 1. A drawing out, or continuing; the act of delaying the termination of a thing; prolongation; continuance; delay; as, the protraction of a debate.

A protraction only of what is worst in life.

Mallock.