586 SYSTEMATIC HISTORY OF THE INFUSOEIA. 



that of nearly every other naturalist, no existence ; the appearances so inter- 

 preted are explicable in a different manner. Adopting the results of recent 

 discoveries, the following descriptive characters may be laid down. 



Body bell-shaped (campaniilate), supported on a highly contractile, un- 

 branched pedicle or stem, and surmounted at its wide upper extremity by a 

 dilated and somewhat everted margin, or '' peristom." The wide anterior 

 extremity is closed by a " disc," fringed with cilia, which commence on one 

 side of a depression or fossa in the peristom, called the vestibulum, whence 

 they ascend to surround the chsc, and after continuing down its sides or 

 " stem," enter the mouth, and thence return to their starting point, thereby 

 completing a spiral ciliary wreath, or rotary apparatus, which serves by its 

 vibrations to di-aw food inwards to the mouth, and, when the animal detaches 

 itself, as an organ of locomotion. The disc may be slightly elevated above 

 the peristom, but less so than in other true Yorticellina ; when so elevated, 

 the ciliary apparatus is said to be expanded. On the other hand, it may be 

 withdi^awn under cover of the peristom, the cilia disappearing from view ; 

 and when more strongly contracted, the whole disc is so drawn mthin the 

 body that the entii^e appearance of the anterior extremity or head of the 

 animal is lost, its ciliary mechanism being so inverted that it appears in- 

 ternally hke an irregular sigmoid cavity, in which the cilia may possibly be 

 distinguishable, whilst the peristom is itself completely closed in upon the 

 whole. In this state of com])lete contraction the Vorticella resembles a shut 

 ovoid sac. Except the head, the rest of a Vorticella is destitute of cilia. 

 The fossa lying between the sides of the ciliary disc and the peristom is the 

 vestibulum, into which both the oral and anal outlets open, within a very 

 short space of one another. The mouth opens below into a ciliated pharynx 

 or oesophagus, which is extended a considerable distance into the interior as 

 a digestive tube, terminating, it would appear, suddenly by an open end. 

 The food received at the mouth is transmitted through the oesophagus, and 

 is formed at its extremity, with the aid of water, into a globule or vacuole, 

 which is pushed onwards by the vis a tergo in a circular course towards the 

 anal outlet. Besides molecules and granules derived from food (vesicular 

 bodies composed of oily or other matters), there are always present in the 

 interior a round contractile vesicle and an elongated curved band- like nucleus, 

 often with several minute clear spaces or nucleoli. The vesicle is usually 

 placed near the lower end of the digestive tube, and the curved, horseshoe- 

 shaped nucleus lies across at the posterior third of the animalcule. The 

 Vorticellce multiply by longitudinal self-division, and by the growth of gemmas 

 from their base, and propagate by the resolution of the nucleus, after encyst- 

 ing itself, into numerous Euglena-like or Monadiform beings, and, according 

 to Stein, by ciliated embryos through the mediiun of a previous conversion 

 into Achietfe. The new beings formed from fission or gemmation are at iii'st 

 in a contracted condition, and on their detachment are found to be furnished 

 with a posterior circlet of cilia to serve as a means of locomotion imtil they 

 . affix themselves and proceed to develope a pechcle, after which it disappears, 

 and the ordinary ciliary wreath of the head unfolds itself. Indeed, even 

 when these processes of multiplication are not in operation, a Vorticella 

 can detach itself and leave its stalk, or swim away T\dth its pedicle when 

 loosened from its hold. 



The pedicle is remarkably contractile, (bawing itself into a close coil with 

 extraordinaiy rapidity, and again uncoiling itself with equal quickness, regu- 

 lating these movements by external conditions, as though possessing con- 

 sciousness and will. The pedicle is a hollow tube, containing a thread or 

 band within it, to which its contractile power is due. 



