60 



POLYGASTRICA. 



spontaneous fissure, or division of the body of an adult animalcule 

 into two or more portions, each of which is perfect in all its parts. 

 This singular kind of generation, by which the old animalcule 

 literally becomes converted into two or more young ones, is 

 accomplished in various ways, which will require separate notice. 



In the oval forms of the polygastrica, the line of separation 

 generally divides the body transversely into two equal portions, 

 by a process, the different stages of which are represented in 

 Jig. 20 ; 1, 2, 3. The body 

 of an animalcule about to di- 

 vide 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 por- 

 tion : a constriction becomes 

 gradually apparent at each 

 extremity of the line of divi- 

 sion, which soon grows more 

 decided, and at length the 

 two parts are only united 

 by a narrow isthmus, {Jig. 

 19, 3,) which, getting thinner 

 and thinner, allows a slight 

 effort on the part of either of 

 the now nearly distinct por- 

 tions to tear itself from the other half, and complete the separation. 



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 occasionally transverse, the newly 

 formed creature appearing truncated at one end (fig. 19, 5) for 

 some time after the completion of the process. 



(86.) The mode of generation in Convallaria, a group of which 

 is seen at fig. 20, 11, is very curious; and from the different 

 forms which the young assume during the progress of develope- 

 ment much confusion has occurred, each stage of its growth having 

 been described as the permanent appearance of a distinct species. 

 This beautiful animalcule seems to be propagated in several 

 ways : sometimes this is effected by external gemmules, which 

 appear like minute points, scarcely more than y^oo of a l me * n 



