MICROSCOPIC FOKMS OF ANIMAL LIFE. 



41 



the approach of winter, the suctorial tentacles and the contractile vesicles 

 disappearing; they do not, however, seem to acquire any special envelope, 

 remaining as clear, motionless, protoplasmic particles. But with the 

 return of warmth their development recommences, a footstalk is formed, 

 and they gradually assume the characteristic form of Podophrya quadri- 

 partita. A regular ' conjugation ' has been observed in this type, the 

 body of one individual bending down so as to apply its free surface to the 

 corresponding part of another, with which it becomes fused (Fig. 302, 1); 

 but whether this always precedes the production of internal embryos, or 

 is any way preparatory to propagation, has not yet been ascertained. J 



435. Ciliata. As it is in this tribe of Animalcules that the action of 

 the organs termed Cilia has the most important connection with the vital 

 functions, it seems desirable here to introduce a more particular notice 

 of them. They are always found in connection with cells, of whose pro- 

 toplasmic substance they may be considered as extensions, endowed in 



FIG. 303. 



Immature forms of Podophrya quadripartita: 1, Amoeboid state (Trichophrya of Clapar&de 

 and Lachmann); 2, The same more advanced; 3, Incipient division into lobes. 



a special degree with its characteristic contractility. The form of the 

 filaments is usually a little flattened, tapering gradually from the base to 

 the point. Their size is extremely variable ; the largest that have been 

 observed being about l-500th of an inch in length, and the smallest 

 about l-13,000th. When in motion, each filament appears to bend 

 from its root to its point, returning again to its original state, like the 

 stalks of corn when depressed by the wind ; and when a number are 

 affected in succession with this motion, the appearance of progressive 

 waves following one another is produced, as when a corn-field is agitated 

 by successive gusts. When the ciliary action is in full activity, however, 

 little can be distinguished save the whirl of particles in the surrounding 

 fluid ; but the #ac&-stroke may often be perceived, when the forward- 



1 The Acinetina were described both by Ehrenberg and Dujardin; but the first 

 full account of their peculiar organization was given by Stein in his " Organ ismus 

 der Infusionsthierchen." Misled, however, by their parasitic habits, Stein origi- 

 nally supposed them not to be independent types, but to be merely transitional 

 stages in the development of Vorticellinae. and other Ciliate Infusoria. This doc- 

 trine he has long since abandoned; but it is not a little singular that the young of 

 several true Ciliata come forth provided with suctorial tentacles as well as with 

 cilia, losing the former as they approximate with advancing growth towards the 

 parental type. Much information as to this group will also be found in the beau- 

 tiful " Etudes sur les Infusoires et les Ehizopodes" of MM. Claparede and Lach- 

 mann, Geneva, 1858-61. 



