Cii THE BEGINNINGS OF LIFE. 



embryos become developed during the 



period of conjugation ^. 

 B. Such development occurring in single individuals, 

 independently of conjugation. 

 a. Animals/)'^^ and active, 



I. Development of embryos out of portions 

 of nucleus, separated by fission or gem- 

 mation, has been seen in Nassula and 

 in Parameciuvi. Four or five embryos 

 are often produced at the same time by 

 this method, though they are discharged 

 singly. Cohn says that, instead of the 

 ordinary Acinetiform embryos, he has 

 frequently witnessed the escape of 

 others, having a globular figure, which, 

 in addition to the tentacles, are pro- 

 vided with cilia over their whole surface. 

 He has, on one or two occasions, seen a 

 fission of the parent animal take place 

 during the very time that embryos of 

 this kind were escaping. 



In Nassula elegans Cohn has also seen 

 embryos developed in a cavity within 

 the body, which was adjacent to 

 the nucleus, and communicated by 

 a narrow canal with the exterior^. 

 After their escape the embryos were 

 motionless and without cilia, though 

 they presented a few knobbed tenta- 

 cular processes. A similar mode of 

 development of embryos has been ob- 

 served in the products of a recent fission 



^ ' Ann. of Nat. Hist.,' 1858, vol. ii. p. 439. 



2 ' Zeitschrift,' 1857, p. 143, and Pritchard's ' Infusoria,' p. 356. 



