PEOPAaATION BY FISSUEE. 



45 



Fig. 20. 



the different stages of which are represented in fig. 20, 1,2, 3. The body 

 of an animalcule about to divide in this manner becomes at first slightly 

 elongated, and a line more transparent than the rest of its body is seen 

 to cross its middle portion : a constriction becomes gradually apparent at 

 each extremity of the line of division ; this soon grows more decided, and 

 at length the two parts are only united by a narrow isthmus (fig. 20, 3), 

 which, getting thinner and thinner, allows a slight effort on the part of 

 either of the now nearly distinct portions to tear itself from the other 

 half and complete the separation. 



(96.) In some elongated species (fig. 20, 4) the fissure is effected in 

 a longitudinal direction, the separation gradually proceeding from the 

 posterior to the anterior 

 extremity of the body 

 (fig. 20, 6) ; yet even in 

 these the division is occa- 

 sionally transverse, the 

 newly-formed creature ap- 

 pearing truncated at one 

 end (fig. 20 , 5) for some 

 time after the completion of 

 the process. 



(97.) The above mode of 

 generation, as exhibited in 

 Vorticella, a group of which is 

 seen at fig. 20, 9, 10, 11, 12, 13, 

 is very curious ; and from the 

 different forms assumed by 

 the young during the progress 

 of their development much 

 confusion has occurred, each 

 stage of growth having been 



described as the permanent appearance of a distinct species. This 

 beautiful animalcule seems to be propagated in several ways. Some- 

 times this is effected by external gemmules, which appear like minute 

 points, scarcely more than y^-th of a line in diameter, upon the pedicles 

 of the adult Convallaria3 ; these in time become pedunculated, and, 

 although still very small, exhibit the cilia upon the margins of the de- 

 licate cups ; in this state they were called by Schrank Vorticdlce mona- 

 dicce (fig. 21). The Yorticelloe generally, however, multiply by fissure, 

 the bell- shaped cup at the extremity of their highly irritable pedi- 

 cles 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. 



(98.) The adult animalcule (seen with its pedicle fully extended, 



