OF THE ROTATORIA. 439 



diately on the part), and rarely pedunculate (/. e. supported on a pedicle or 

 Btem), as in Otoglena. In some species, as in Rotifer, the eyes are placed 

 on a protrusile part of the head, and consequently appear at one time in ad- 

 vance of the head, and at another far backward mthin the body. In Monura, 

 Ehrenberg states they are moveable. The number of eye-spots varies con- 

 siderably : in several genera there is but one, e. g. Fiircularia, 3Ionocerca, 

 Notommata, and Brachiomis ; but two eyes are more common, as in Melicerta 

 (XXXYII. 15), Lacinidaria, Megahtrocha (XXXII. 376), Botifer (XXXV. 

 476-478), and Diglena ; three eye-specks occur in Asplanchna, TriophthaU 

 mus (XXXIII. 412—414), EospJiora, and Otoglena ; four in SquameUa ; and 

 from six to twelve coloured spots and upwards are met with in Cydoglena and 

 Theorus (XXXIY. 425-429), but their visual character is more than doubt- 

 ful. These last " conglomerate eyes," as Ehrenberg calls them, appear to 

 be no other than collections of coloured (it may be oil) particles, and are 

 akin to the large coloured spaces seen on Notommata forcipata and Synchceta 

 Baltica, having neither a definite nor a regular outline (see p. 440). Subse- 

 quent research has proved Ehrenberg in error respecting the number of eyes 

 in several species, — an error which seriously affects his classification. 



The ordinary colour of the eye-specks is red, but sometimes it is reddish- 

 brown, and rarely violet or black. The coloiu- may change in the lifetime of 

 the individual, as from red in the young to black in the adult state. In a 

 few instances no eye-specks are visible. 



Except some of the doubtful collections of coloured specks, the eye-spots are 

 placed immediately above the great ganglion of the head, the homologue of the 

 brain, or, as Siebold affirms, are united with it by intermediate nerve-fibres. 

 The intimate structure of the eyes was iU-understood by the great Prussian 

 Professor. He was unable to convince himself of the existence of a cry- 

 staUine lens and of a cornea. Thus, in his account of Rotifer' vulgaris, he 

 states that the eyes consist of several cells filled with a granular pigment, 

 and sometimes they separate abnormally into several portions. He thinks 

 there is no crystalline lens, although they are probably compound, like the 

 eyes of insects. 



Siebold insisted on the coloured specks of Rotatoria being sharply defined, 

 and in many cases, at least, furnished with a capsule, in contradistinction to 

 the ill-defined vanishing pigment-masses imagined to be eyes in the Protozoa. 

 Wagner also speaks of a lens in the eyes of Lacinularia. Perty is adverse 

 to the notion of a lens or cornea, or of a capsule ; yet in Pteivdina Patina 

 he notes that the elliptical eye-speck, viewed on the side and from below, is 

 seen to consist of an upper red and an under white half. That the latter 

 represents a refracting medium is highly probable. A compound structure 

 is further indicated by Perty in Scaridium longicaudum, in which he perceived 

 '^ a mass of small granules resembling a gland, in the midst of the red pig- 

 ment-corpuscles, which are outspread irregularly, and paler at the circum- 

 ference. Moreover, in Euchlanis triquetra there is an irregular brown scale 

 with reddish-brown contents, whilst in E. Luna the unusually large eye-spot 

 appears to be made up of ten to twelve distinct red granules. 



^ Leydig arranges the single eye-specks under three types : — 1. an ordinary 

 pigment-spot, of a rounded or irregular outline, a reddish-brown, black, or 

 \iolet colour, not shar]^)ly defined, e. g. in Notomynata Synchceta ; 2. a de- 

 fined, sharply-bounded speck, actually composed of two coalesced hemi- 

 spherical portions, such is seen in Brachiomis ; 3. a speck having a clear 

 refracting body projecting from the mass of pigment — a stnicture discovered 

 by Leydig in Euchlanis unisetata (XXXVIII. 19). The first type is the most 

 prevalent. 



