22 INFUSORIA. 



effort on the part of either of the now nearly distinct portions is 

 sufficient to sever the frail bond of union and complete the sepa- 

 ration. In some elongated species this fissure is effected in a 

 longitudinal direction, the separation gradually proceeding from 

 the posterior to the anterior portion of the body. Examples of 

 both these modes of increase are delineated in the appended 

 engravings (Fig^. 12 and 13). 



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 through 

 all parts of the soft texture of their bodies, this kind of spon- 

 taneous division would be a very simple matter, and every step 

 of the process easily understood ; a little observation, however, 

 will show that there are circumstances attending this operation 

 of a very inexplicable character. Some species, as for example, 

 Prorodon teres* represented in our engraving (Fig. 12, b), are 

 furnished with a very curious mouth surrounded by a cylinder 

 composed of horny teeth, through the agency of which their food 

 is seized and swallowed. Should a deed of separation, therefore, 

 have to be drawn up preparatory to the act of division, it might 

 be a puzzling question for the infusorial lawyers to settle which 

 half should have the mouth. Even this difficulty has, however, 

 been provided for ; and, accordingly, a new mouth and a new 

 dental cylinder is seen to sprout from the hinder half, before the 

 animal, originally one flesh, proceeds to divorce itself into two. 



This mode of propagation, in which multiplication and division 

 go hand in hand, is amazingly productive, and, indeed, far sur- 

 passes in fertility any other with which we are acquainted. Every 

 schoolboy is familiar with the celebrated problem about the nails 

 in a horse's shoes, or the squares of a chess-board, where the re- 

 sults attainable by duplicative multiplication soon pass ordinary 

 numerical expressions. Let any of our readers try the same 

 problem with one of these animalcules. An individual, if well 

 supplied with food, has been observed to divide at least once in 

 twenty-four hours. So that in a fortnight, allowing the product 

 of each division to multiply at the same rate, sixteen thousand 

 three hundred and eighty-four would be produced from the same 

 stock, and in four weeks two hundred and sixty-eight millions 

 four hundred and thirty-five thousand four hundred and fifty-six, 

 would be the astounding progeny derived from a single animalcule. 



* TrpJjpa, prora, fore part ; odbvs, cdbvros, odous, odontos, a tooth- 



