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.] (Zoöl.) 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 Vorticellæ. The reproduction takes place by fission, or by the breaking up of the contents of the body

(Pro*top"o*dite) n. [Proto- + Gr. foot.] (Zoöl.) The basal portion, or two proximal and more or less consolidated segments, of an appendage of a crustacean.

(Pro"to*pope) n. [Proto- + pope: cf. F. protopope, Russ. protopop'.] (Gr. Ch.) One of the clergy of first rank in the lower order of secular clergy; an archpriest; — called also protopapas.

(||Pro*top"te*rus) n. [NL., from Gr. first + a feather ] (Zoöl.) See Komtok.

(Pro"to*salt) n. [Proto- + salt.] (Chem.) A salt derived from a protoxide base. [Obs.]

(Pro`to*sil"i*cate) n. [Proto- + silicate.] (Chem.) A silicate formed with the lowest proportion of silicic acid, or having but one atom of silicon in the molecule.

(Pro`to*so"mite) n. [Proto- + somite.] (Zoöl.) One of the primitive segments, or metameres, of an animal.

(Pro`to*sul"phide) n. [Proto- + sulphide.] (Chem.) That one of a series of sulphides of any element which has the lowest proportion of sulphur; a sulphide with but one atom of sulphur in the molecule.

(Pro`to*sul"phu*ret) n. [Proto- + sulphuret.] (Chem.) A protosulphide. [Obs.]

(||Pro`to*the"ri*a) n. pl. [NL., from Gr. prw^tos first + qhri`on, dim. of qh`r beast.] (Zoöl.) Same as Monotremata.

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

(Pro"to*type) n. [F., from L. prototypus original, primitive, Gr. first + type, model. See Proto- , and Type] An original or model after which anything is copied; the pattern of anything to be engraved, or otherwise copied, cast, or the like; a primary form; exemplar; archetype.

They will turn their backs on it, like their great precursor and prototype.

(Pro`to*ver"te*bra) n.; pl. Protovertebræ . [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 protovertebræ were long regarded as rudiments of the permanent vertebræ, 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 protovertebræ.

(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).

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