CILIATA 



775 



food, with its cilia in active vibration, the stalk is fully extended. 

 If, however, the animalcule should have drawn to its mouth any 

 particles too large to be received within it, or should be touched by 

 any other that happens to be swimming near it, or should be 

 ' jarred ' by a smart tap on the stage of the microscope, the stalk 

 suddenly contracts into a spiral, from which it shortly afterwards 

 extends itself again into its previous condition. The central cord, 

 to whose contractility this action is due, has been described as 

 muscular, though not possessing the characteristic structure of either 

 kind of muscular fibre ; it possessed,, however, the special irritability 

 of muscle, being instantly called into contraction (according to the 

 observations of Kiihiie) by electrical excitation. The only special 

 * impressionable ' organs l for the direction of their actions with the 

 possession of which Infusoria can be credited are the delicate 

 bristle -like bodies which project in some of them from the neighbour- 

 hood of the mouth, and in titentor from various parts of the surface. 

 The red spots seen in many Infusoria, which have been designated 

 as eyes by Professor Ehrenberg, from their supposed correspondence 

 with the eye-spots of Rotifera, really bear a much greater re- 

 semblance to the red spots which are so frequently seen among 

 protophytes. R. Hertwig, who seems to have successfully defended 

 himself against the strictures of Professor Vogt, has described a 

 vorticellid Erythropsis agilis as having a pigment-spot which 

 cannot but be regarded as a rudimentary eye ; Metschnikoff, who 

 thinks that Eryihropsis is an Acinetan, found a similar form with a 

 similar eye near Madeira ; and Harker observed that if light be 

 allowed to fall on a part only of a colony of Ophridium versatile all 

 the members soon congregate to the illuminated portion. 2 



The interior of the body does not always seem to consist of a 

 simple undivided cavity occupied by soft protoplasm ; for the tegu- 

 mentary layer appears in many instances to send prolongations 

 across it in different directions, so as to divide it into chambers of 

 irregular shape, freely communicating with each other, which may 

 be occupied either by protoplasm, or by particles introduced from with- 

 out. The alimentary particles which can be distinguished in the 

 interior of the transparent bodies of Infusoria are visually proto- 

 phytes of various kinds, either entire or in a fragmentary state. 

 The Diatomacere seem to be the ordinary food of many ; and the 

 insolubility of their loricce enables the observer to recognise them 

 unmistakably. Sometimes entire Infusoria are observed within the 

 bodies of others not much exceeding them in size (fig. 597, B) ; but 

 this is only when they have been recently swallowed, since the prey 

 speedily undergoes digestion. It would seem as if these creatures 

 do not feed by any means indiscriminately, since particular kinds of 

 them are attracted by particular kinds of aliment ; the crushed 

 bodies and eggs of Entomostraca, for example, are so voraciously 



1 The term ' organs of sense ' implies a consciousness of impressions, with which 

 it is difficult to conceive that unicellular Infusoria can be endowed. The component 

 cells of the human body do their work without themselves knowing it. 



2 These results are confirmed by the observations of R. Franze ; see Zeitschr. 

 wiss. ZooL Ivi. 1893, pp. 138-64. 



