s. 157. _Greek._--Words derived _directly_ from the Greek are in the same predicament as the Latin of the third period--_phaenomenon_, _phaenomena_; _criterion_, _criteria_, &c.; words which are only _indirectly_ of Greek origin, being considered to belong to the language from which they were immediately introduced into the English. Such are _deacon_, _priest_, &c., introduced through the Latin; thus a word like _church_ proves no more in regard to a Greek element in English, than the word _abbot_ proves in respect to a Syrian one. s. 158. The Latin of the fourth period and the Greek agree in retaining, in many cases, the Latin or Greek inflexions rather than adopting the English ones; in other words, they agree in being but _imperfectly incorporated_. The phaenomenon of imperfect incorporation (an important one) is reducible to the following rules:-- 1. That it has a direct ratio to the date of the introduction, _i.e._, the more recent the word the more likely it is to retain its original inflexion. 2. That it has a relation to the number of meanings belonging to the words: thus, when a single word has two meanings, the original inflexion expresses one, the English inflexion another--_genius_, _genii_, often (_spirits_), _geniuses_ (_men of genius_). 3. That it occurs with substantives only, and that only in the expression of number. Thus, although the plural of substantives like _axis_ and _genius_ are Latin, the possessive cases are English. So also are the degrees of comparison, for {103} adjectives like _circular_, and the tenses, &c. for verbs, like perambulate. s. 159. The following is a list of the chief Latin substantives, introduced during the latter part of the fourth period; and, preserving the _Latin_ plural forms-- FIRST CLASS. _Words wherein the Latin Plural is the same as the Latin Singular._ (_a_) _Sing._ _Plur._ (_b_) _Sing._ _Plur._ | Apparatus apparat_us_ | Caries cari_es_ Hiatus hiat_us_ | Congeries congeri_es_ Impetus impet_us_. | Series seri_es_ | Species speci_es_ | Superficies superfici_es_. SECOND CLASS. _Words wherein the Latin Plural is formed from the Latin Singular by changing the last Syllable._ (_a_).--_Where the Singular termination _-a_ is changed in the Plural into _-ae__:-- _Sing._ _Plur._ | _Sing._ _Plur._ | Formul_a_ formul_ae_ | Nebul_a_ nebul_ae_ Lamin_a_ lamin_ae_ | Scori_a_ scori_ae_. Larv_a_ larv_ae_ | (_b_).--_Where the singular termination _-us_ is changed in the Plural into _-i__:--