POLYGASTRIA. 21 



diffused, as in Leucophrys {fig. 13.), Loxodes (/ig. 18), Bursaria, Nds- 

 sula ; sometimes aggregated in longitudinal rows, as in Amph'deptits ; 

 or in transverse circles along narrow bands, as in Trichodina ; or they 

 are limited to the region of the mouth,.as in the Vorticellce, {Jig. 5.), in- 

 dicating the passage to the higher or Rotiferous group. The body in 

 Peridinium is girt with an oblique hoop of long cilia. In most Polygas- 

 tria the cilia are longer than they are commonly represented, and the 

 marginal cilia of the flat body in Stylonychia, and the ventral ones in 

 Oxytricha and Euplotes, 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. In some 

 Polygastria cilia are supported on one {Amblyophis) or two {Chlorogo- 

 nmm) tentacular processes, which wave to and fro and create currents 

 in the water ; in Peridinium tripos there are three such prolonga- 

 tions ; but true jointed locomotive members are never developed in 

 any of this minute and primitive race of animated beings. They retain, 

 throughout life, those simple vibratile organs which produce the ro- 

 tatory movements in the ova of Mollusca whilst imprisoned in their 

 nidus, which are the agents of analogous movements of the Mamma- 

 lian ovum in the fallopian tube, and which are probably common to 

 the embryos 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 on a greater or less proportion of the mucous 

 surfaces of all animals, most probably vibrate by virtue of the con- 

 tractility of their tissue. Ehrenberg, however, directs attention to 

 their expanded base in some Polygastria, and especially to a radiated 

 structure there which he conceives to indicate the disposition of the 

 muscular fibres moving such cilia. 



In observing the motions of the Polygastric Infusoria, one per- 

 ceives 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, or entangle and inclose by those organs.* But 

 the greater number of the class subsist on the minute atoms of the 

 decomposing animal and vegetable substances of the fluids or in- 

 fusions in which they exist, — particles which do not require a 

 definite pursuit, since they are inert and generally diffused through- 

 out the infusion. 



* XIX p. 202. 

 C 3 



