INFFSORTAt ANIMAtCTTtES. 33 



less locomotive ; but, especially in the family Bacilhria, there are 

 manj' motionless genera. In Volvox we see a rolling motion, often 

 very lively ; in Bodo and Colcjjs a leaping movement, very active ; 

 in Amceha and Bifflncjia, a crawling, most nearly resembling that of 

 snails ; in Styhnychia, Euplotes, and Rimantophorm, a creeping, by 

 means of uncini, or bristle-like cilia, like that of insects ; whilst in 

 very many there is a eimple gliding or swimming motion, in some, 

 accompanied by rotation on their axis, and in others, of greater 

 relative length, by writhing or serpentine movements ; these last 

 varieties are illustrated in Paramecium, Uroleptus, Trachelocerca, La- 

 crymaria. Lencophrys, Stentor, Spirostomum, &c. In very minute 

 forms, as the Vihrionia, their movements are visible, as scintillations 

 in the containing fluid. 



Generally speaking, in all the Polyyastrica, with the exception of 

 i^& Pseudopoda, — those with soft * variable processes,^ and the Closterina 

 and BacilJaria {Destnidiece and Biatome<e), the property of movement 

 is conferred by cilia, or by varieties of them called proboscides, or by 

 stiff processes — uncini, &c (see Section II.) but in none ai'e found 

 ti'ue jointed locomotive members. 



Prof. Owen remarks, in his Lectures on the Comparative Anatomy 

 and Physiology of the Invertebrated Animals, 1843, p. 19, " 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 move- 

 ments." Further on, he wi'ites : " The motions of the Polygastrica 

 have appeai'ed to me, long watching them for indications of volition, 

 to be in general of the natiu'e of respiratory acts, rather than attempts 

 to obtain food or avoid danger. Very seldom can they be construed 

 as voluntary, btit seem rather to be automatic ; governed by the 

 influence of stimuli -within or without the body, not felt, but re- 

 flected upon the contractile fibre ; and, therefore, are motions which 

 never tire. We may thus explain the fact which Ehrenberg relates 

 — not without an expression of surprise — namely, that at whatever 

 period of the night he examined the living Infusoria, he invariably 

 found them moving as actively as in the day time ; in short, it seemed 

 to him that these little beings never slept." 



The power of locomotion may be for a time possessed by Infusoria,. 



