POLYGASTIUCA. 61 



diameter, upon the pedicles of the adult convallarise ; these in time 

 become pedunculated, and, although still very small, exhibit the 

 cilia upon the margins of their delicate cups ; in this state they 

 were called by Schrank Vorticella monedicce. The Convallarise 

 generally however multiply by fissure, the bell-shaped cup at the 

 extremity of their highly irritable pedicles separating longitudinally 

 into two ; but the progress of this division requires our particular 

 notice, as the unpractised observer might be considerably puzzled 

 on witnessing some of the phenomena attending it. 



The adult animalcule, seen with its pedicle fully extended, 

 (Jig. 20, 9,) when it is alarmed, shrinks by throwing its stem into 

 spiral folds (10) : in the latter figure, the bell or body of the 

 animalcule is seen to have extended considerably in breadth, pre- 

 paratory to its becoming divided into two distinct creatures. At 

 11, the commencement of its division is depicted; the separation 

 gradually extending from the base, or ciliated extremity, to the 

 point where the body is attached to its stem. When the division 

 has extended thus far, (12,) the newly formed portion is seen with 

 surprise to have become furnished with cilia at both ends, and, 

 when finally detached, (13,) only at the opposite extremity to 

 that on which they originally existed ; it then, freed from its pe- 

 dicle, and thus losing the great characteristic of its species, swims 

 about at large, exhibiting forms represented at 14, 15, 16, 17, all 

 of which have been described as distinct species by different 

 writers ; at last it puts forth a new stem, and, assuming the adult 

 form, becomes fixed by its pedicle to some foreign body. 



(87.) This fissiparous mode of reproduction is amazingly pro- 

 ductive, and indeed far surpasses in fertility any other with which 

 we are acquainted, not excepting the most prolific insects or even 

 fishes. Thus the Paramecium aurelia, if well supplied with 

 food, has been observed to divide every twenty-four hours, so that 

 in a fortnight, allowing the product of each division to multiply at 

 the same rate, 16,384 animalcules would be produced from the same 

 stock ; and in four weeks the astonishing number of 268,435,456 

 new beings would result from a continued repetition of the process : 

 we shall feel but little surprise, therefore, that with such powers of 

 increase these minute creatures soon become diffused in countless 

 myriads through the waters adapted to their habits. 



(88.) The capability of spontaneous division is one of the most 

 distinctive attributes of the acrite type of structure ; and was the 

 organization of these animalcules as simple as it was supposed to 



