438 GENERAL HISTORY OF THE INFUSORIA. 



on the neck, its obseiTer is inclined to refer to the same category with the 

 problematical structui'es of Euclilanis and Notommata centrura. He more- 

 over seeks to establish an affinity between these organs and the small clear 

 space sui'mounted by a ring on the cuticle, situated in the middle line of the 

 body, behind the frontal speck in Phyllopoda, such as Branchipus ; but even 

 if this affinity be admitted, no light is thrown upon the functions of these 

 questionable structures. 



b. Organs of Sense. — The existence of some of the senses is to be in- 

 ferred from that of a nervous system. The sense of touch is one concerning 

 which there can be no question ; that of taste, in its nature allied to the 

 tactile sensibility, is very doubtful, whilst those of smelling and heaiing may 

 be pretty safely stated to be entii-ely absent. Lastly, the sense of sight 

 is generally admitted to exist, and to have special organs, or eyes, for its 

 exercise. 



Touch may be supposed to be diffused as common sensibility over the 

 entire surface of the body, and especially developed in the soft tissue of the 

 rotary organ, in its processes and antennae, and in the soft processes and 

 termination of the pseudopodium. Something approaching a sense of taste 

 has been imagined present, particularly in the antennae or feelers. If the 

 faculty of hearing seems occasionally exercised, we must attribute the cir- 

 cumstance in part to the perception of the disturbing cause by vision, and in 

 part to the vibrations produced in the hquid. 



The visual organs (XXXVIII. 16-19, 33) have claimed particular atten- 

 tion, and now have their existence in the majority of Eotatoria, at some pe- 

 riod of their life, satisfactorily proved. Dujardin, dissatisfied with Ehrenberg's 

 hasty generalizations, and compelled to deny the visual character of the co- 

 loured specks in various Protozoa and Phytozoa, looked, no doubt, with greater 

 scepticism upon the Berlin Professor's representations of eyes in Eotatoria 

 than he othei-wise would have done, and started some objections against them. 

 He says — " I wiU not deny a certain analogy between the red specks and the 

 colonized points observed in CydopidcB, and which may be caUed eyes ; but I 

 cannot assign to such specks a very high importance, seeing that they con- 

 stantly disappear in the adult condition of many Rotifera, and otherwise show 

 themselves more distinctly, according to the degree of development as deter- 

 mined by the season and the place of development." It should be noted, 

 however, in reply to this objection, that a similar disappearance, on the at- 

 tainment of the adult state, occurs in the parasitic Crustacea, the visual cha- 

 racter of whose eye- specks or ocelli is not questioned. Moreover, although 

 some coloured specks in the Rotifera are undoubtedly mere heaps of granules, 

 yet others have assuredly a definite optical organization and function. These 

 possess a refracting medium, the essential part of an eye ; and theii' organ- 

 ization, though simple and imperfect, yet elevates them to the rank of eyes, 

 eyelets, or oceUi. 



Ehrenberg gave much attention to the position, nimiber, and other pecu- 

 liarities of the eye-specks of Rotatoria, as he employed them largely in 

 framing his classification. Unfortimately, however, he cUd not acquaint him- 

 self sufficiently with their minute structiu'e, but was content to call all the 

 coloiu^ed specks he met with eyes, and insisted on unimportant and inconstant 

 particulars as generic and specific characteristics. These errors have conse- 

 quently much vitiated his classification {see chapter on Classification) ; and 

 the tendency at the present day is to assign to the coloiu'ed eye-spots an al- 

 together secondary rank among the characteristics of Rotatoria. 



Ehrenberg described the eye- specks as variously situated, on the fore part 

 of the head (forehead) or on the neck, as mostly sessile (?. e. situated imme- 



