The facts set forth in the preceding memoir are to a large extent summarised by the plates which accompany it, and the explanatory description of those plates.
The more general conclusions to which our observations tend may be gathered from the following tabular arrangement of some of the chief varieties of Arthropod eyes which are at present known. The technical terms which have been introduced in the present memoir and recur in the tabular statement are explained in a list appended.
Without assuming to assign their due significance to all varieties of the Arthropod eye, some of which may very possibly (e. g. those of certain Crustacea) find no proper place in the scheme here submitted, we yet think that it is useful to tabulate the principal facts of structure known as to a large number of Arthropod eyes in the following way.
We take as primary divisions those eyes with monostichous ommateum, the more archaic, and those eyes with diplostichous ommateum derived from the monostichous condition. A few examples clearly transitional between the monostichous and the diplostichous condition have been described by Grenadier (among Myriapods).
It is especially to be noted in reference to the comparison of monomeniscous and polymeniscous eyes, that the comparison yields totally different results accordingly as we may choose to compare with the non-facetted eye of a Spider or of an Insect larva, on the one hand, a single eyelet of a "grouped" eye or of a "compound" eye, or on the other hand, the whole group or the whole "compound" eye.