POLYGASTRIA. 19 



The locomotive Polygastria propel themselves througli the water by 

 the action of their vibratile cilia, which are sometimes generally dif- 

 fused, as in Bursaria and Nassula ; sometimes aggregated, in longi- 

 tudinal rows, as in Amphileptus ; often limited to the region of thg 

 mouth, as in the Vorticellce, indicating the passage to the higher or 

 Rotiferous group. These cilia in some species, as in Stylonychia and 

 Eiiplotes, are of such relative size as to give the species a myriapodous 

 character, and are used, like little feet, to creep along the stems of the 

 Chara, and other minute vegetable plants. True jointed locomotive 

 members are never developed in any of this minute and primitive race 

 of animated beings ; but they retain, throughout life, those simple 

 vibratile cilia which produce the rotatory movements in the ova of 

 Mollusca whilst imprisoned in their nidus, which are probably the 

 agents of analogous movements of the ovum of the Mammalia in the 

 Fallopian tube, and which are doubtless common to the ova of all 

 classes of animals at that early period which the Polygastric Infusoria 

 seem permanently to represent. 



These cilia, the outward instruments of locomotion in Infusoria, 

 and which are retained in greater or less proportion on the epithelium- 

 clad mucous surfaces of all animals, appear, notwithstanding their 

 minute size and incalculable numbers, to owe their motions to the 

 actions of definitely arranged muscles : Ehrenberg has seen the ex- 

 panded base of the locomotive cilium in the Polygastria, and describes 

 the radiated structure which he conceives to indicate the disposition 

 of the muscular fibres moving such cilium. 



If you watch the motions of the Polygastric Infusoria, you will 

 perceive that they avoid obstacles to their progress ; rarely jostle one 

 another; yet it is difficult to detect any definite cause or object of 

 their movements. Some species, it is true, prey upon animalcules of 

 their own class, and will gorge an individual of nearly their own 

 size, which they attract by the currents in the water caused by the 

 oral vibratile cilia. But the greater number of the class subsist on 

 the minute atoms of the decomposing animal and vegetable substances 

 of the fluids or infusions in which they exist, — particles which do 

 not require a definite pursuit, since they are inert and generally 

 diffused throughout the infusion. 



The motions of the Polygastria have appeared to me, long watching 

 them for indications of volition, to be in general of the nature of 

 respiratory acts rather than attempts to obtain food or avoid danger. 

 Very seldom can they be construed as voluntary, but seem rather to 

 be automatic ; governed by the influence of stimuli, within or without 

 the body, not felt, but reflected ujjon the contractile fibre ; and 

 therefore are motions which never tire. We may thus explain the 



c 2 



