Text-book of comparative anatomy . idce show peculiarities. They possess twopairs of compound eyes, one frontal pair and one in the region of the cheek. Thetwo eyes of the same side, however, must have proceeded by division from the singleeye of the Amphipoda which in the Hypcridcc is very large superficially. Structure of the Eyes.—The unpaired eye was formerly describedas an x-shaped eye-spot, with or without a refractive body. Onaccount of its general distribution in the Entomostraca, it is also calledthe Entomostracan eye. Its structure will be best illustrated bymeans of an example. The f
Text-book of comparative anatomy . idce show peculiarities. They possess twopairs of compound eyes, one frontal pair and one in the region of the cheek. Thetwo eyes of the same side, however, must have proceeded by division from the singleeye of the Amphipoda which in the Hypcridcc is very large superficially. Structure of the Eyes.—The unpaired eye was formerly describedas an x-shaped eye-spot, with or without a refractive body. Onaccount of its general distribution in the Entomostraca, it is also calledthe Entomostracan eye. Its structure will be best illustrated bymeans of an example. The frontal eye of Calanella mediterranea (Fig. 237), a , consists of 3 single eyes united together, 1 unpaired medianand ventral, and 2 lateral and dorsal. Each single eye is composedof a pigment cup and a strongly refractive transparent lens laid inand on it. The term lens is, however, not applicable. It iscomposed of several cells, each of which is connected, whether at its CR US TA CEA—XEXSOR Y QUO A A~,s 353. FIG. 237.—Eye of Calanella mediter- outer or inner side is not yet quite certain, with a fibre of the opticnerve, and must therefore be considered as a retinal cell. The great similarity in structure betweensuch a single eye and the eyes of Platodesshould not be overlooked. The three-foldstructure of the unpaired Crustacean eye seemsto be characteristic. Occasionally, inUrmicJiipus, 3 separate nerves leave the brainto run to the 3 single eyes. The structure of the paired lateraleyes of the Crustacea (stalked and un-stalked) is much more have here the compound eye socharacteristic of the Arthmpnili. Eventhough, in single divisions of theCrustacea, it presents important modi-fications and complications in itsstructure, we nevertheless evidently have to do (with a few exceptions to ranea $ juv, from below (after Gren-be mentioned later) with homologous acher). p, Pigment plates of the paired;^, -i T i r -i of the unpaired portion;
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
