DOCTRINE OF THE ACINETYV-rORMS. 99 



most part in curved lines, in the course of wliich the 

 motile segment appeared to seek the illuminated side of the 

 drop of water. Cilia could not be perceived over the whole 

 surface (fig. 3'). The contractile space during the move- 

 ments was always in front. The motions were rapid, but 

 still such as to allow of their being followed with a mag- 

 nifying power of 370 diam. After waiting patiently for 

 twenty minutes I saw the motion cease, and at the same 

 time short tentacles made their appearance, which were pro- 

 truded more and more, and in a few minutes afterwards the 

 segment regained the spherical form ; thus, after moving 

 about freely for a time, it was again transformed into a 

 Podoj)hri/a. 



This process of division was witnessed by other observers. 

 It takes place more especially when sufficient nutriment is 

 supplied by numerous Stylonychice to the Podopkryce. The 

 Podophrya does not always di\dde into two equal halves — the 

 segments are more frequently luiequal. After repeated divi- 

 sion the specimens always become more transparent. 



If PodophryfB are alloAved to remain for several days upon 

 the object-glass, and care is taken not to let the water dry 

 up, every stage towards the quiescent condition — that is to 

 say, towards the " encysting " — may be followed. 



In Podophrya, this process takes place in the following 

 manner : On the surface of the body a gelatinous mucous 

 layer appears to be secreted, through which the tentacles 

 pass (fig. 4) . The tentacles disappear in the neighbourhood 

 of the peduncle, and the gelatinous layer in this situation 

 hardens into a loose, transversely plicated membrane ; whilst 

 at the upper end it is still soft, and the tentacles clearly visi- 

 ble (fig. 5). Ultimately these also are retracted, and the 

 entire body of the PodopJirya is enveloped in a wide, loose 

 membrane; the plications are caused by parallel, annular 

 constrictions, placed at equal distances apart and separated 

 by circular, angular or rounded ridges ; these plications are 

 in a plane perpendicular to the peduncle. At the summit of 

 the Podophrya, and often also at the base, the membrane 

 presents deep depressions (figs. 7, 6) ; the enclosed body 

 of the Podophrya acquires on its surface a sharply defined 

 smooth membrane ; whilst the contents of the body become 

 somewhat opaque, enclosing a roiuid clear space (figs. 6, 7, 8) . 

 The Podophrya-cyst thus formed is supported by a peduncle, 

 which is widened at the base. In many instances in which 

 the membrane was not plicated, but loosely enclosed the 

 Podophrya like a sac, I noticed that the peduncle of the cyst 

 was continued uninterruptedly into the membrane, of which 



