What's the difference between differentia and differentiae?

Differentia

Definition:

(n.) The formal or distinguishing part of the essence of a species; the characteristic attribute of a species; specific difference.

Example Sentences:

(1) The testes and vasa differentia from 32 autopsy cases, ranging in age from 26 weeks gestation to 7 years of age, were used to evaluate normal development and morphology of the vas deferens, epididymis and embryonal remnants.
(2) He sees no solid basis for grounding the scope of moral obligations on simple sentience, membership in the human species, or technical differentia such as viability, and concludes that medical ethics still suffers from the lack of an adequate theory on which to base a right to life.
(3) Even for those muscles where a tense-lax difference was found, the data do not support the notion that tension was a necessary of sufficient differentia of production.
(4) Human behavior--from its most elementary states up to its most exquisite differentiae--is certainly determined by egoism.
(5) The quantitative analysis of the rheoencephalographic curves made of the method of differentia, the data being compared one hour before the general anesthesia, during the stage of surgical anesthesia and one hour after it.
(6) The results of perimetry especially of profile perimetry is in cases of achromatopsia so typical and unmistakable that it can be referred to for the differentia.

Definition:

Example Sentences:

(1) The testes and vasa differentia from 32 autopsy cases, ranging in age from 26 weeks gestation to 7 years of age, were used to evaluate normal development and morphology of the vas deferens, epididymis and embryonal remnants.
(2) He sees no solid basis for grounding the scope of moral obligations on simple sentience, membership in the human species, or technical differentia such as viability, and concludes that medical ethics still suffers from the lack of an adequate theory on which to base a right to life.
(3) Even for those muscles where a tense-lax difference was found, the data do not support the notion that tension was a necessary of sufficient differentia of production.
(4) Human behavior--from its most elementary states up to its most exquisite differentiae--is certainly determined by egoism.
(5) The quantitative analysis of the rheoencephalographic curves made of the method of differentia, the data being compared one hour before the general anesthesia, during the stage of surgical anesthesia and one hour after it.
(6) The results of perimetry especially of profile perimetry is in cases of achromatopsia so typical and unmistakable that it can be referred to for the differentia.