46 INFUSORIA. 



fig. 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, preparatory 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 becomes freed from its 

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

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



(99.) This fissiparous mode of reproduction is amazingly productive, 

 and indeed far surpasses in fertility any other with which we are ac- 

 quainted, not excepting the most prolific insects or even fishes. Thus 

 a Paramecium, 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 num- 

 ber of 268,435,456 new beings would result from a continued repetition 

 of the process : we therefore feel but little surprise that, with such 

 powers of increase, these minute creatures soon become diffused in count- 

 less myriads through the waters adapted to their habits. 



If the organization of these animalcules were as simple as it was 

 supposed to be a few years ago, when they were thought to be mere 

 specks of living jelly, imbibing nourishment at every point of their 

 surface, which became diffused through all parts of the homogeneous 

 texture of their bodies, their spontaneous division would be perfectly 

 intelligible, and every step of the process easily understood ; but, setting 

 aside the conformation of their digestive apparatus, there are many cir- 

 cumstances attending the operation indicative of a power of developing 

 new organs in the construction of every fresh individual, which must 

 be looked upon as a very interesting feature in their history. Thus 

 a new oral orifice, surrounded with cilia, must be formed upon the 

 posterior segment of each divided animalcule. In Nassula elegans 

 the curious dental apparatus, complex as its structure seems to be, 

 must be developed upon the new part of the body preparatory to every 

 separation ; and accordingly a new mouth or dental cylinder is actually 

 seen to sprout from the hinder half of the creature before its transverse 

 fissure is complete. 



(100.) Nearly all the Infusoria and Rhizopoda have in their interior 

 a kind of nucleus, which is quite different in its compact texture from 



