Dr. C. F. J. Lachmann on the Organization of Infusoria. 231 



ation. Stein gives an incorrect represertation of the fissation 

 of the Vorticellince, as he supposes that before this takes place 

 the ciliary disk, oesophagus, &c. of the old animal are absorbed, 

 and when the fissation has advanced further, two new ciliary 

 disks are formed. This, however, is not the case : by careful 

 observation the movement of the cilia is seen, during the whole 

 process of fissation, upon the ciliary apparatus, and in the vesti- 

 bulum and oesophagus of the animal which is closed up by the 

 peristome. 



Fissation had not been previously observed in the family of 

 the Acinetina, and it has only been very recently described by 

 Cienkowsky * in Podophrya fixa ; one of the two buds of fissa- 

 tion acquires cilia all over it, retracts its suckers, and swims 

 away, becoming again converted into a Podophrya by the 

 loss of its cilia; the same thing takes place in Acineta my- 

 stacina, and here also one of the buds of fissation is ciliated 

 all over. 



Far less general than fissation is the process of gemmation, 

 which is only known as yet in Vorticellince, Acinetina (here only 

 in Dendrosoma radians, Ehrbg.), and in Spirochona gemmipara, 

 Stein, the position of which still appears doubtful to mef- In 

 the Vo7-ticellincE the bud is formed as a swelling of the paren- 

 chyma on some part of the body, into which a diverticulum of 

 the digestive cavity of the parent animal extends. The alimen- 

 tary cavity of the bud thus formed is subsequently divided from 

 that of the mother, and finally the entire bud separates, with de- 

 velopment of a posterior circlet of cilia. In Dendrosoma radians, 

 Ehrbg., a branch of the nucleus grows into the bud whilst it 

 still remains united to the parent animal. Fissation and gem- 

 mation pass into each other almost imperceptibly, as the buds 

 of gemmation are not always much smaller than their parent ; 

 if it be desired to draw a sharp line of demarcation between 

 them, we may say that in fissation each of the new-formed ani- 

 mals acquires a pre-existing part of the nucleus of the old ani- 

 mal; whilst in gemmation, one part, the bud, only acquires a 

 newly-formed part of the old nucleus, or none at all ; (in the lat- 

 ter case, of course, a nucleus must be developed independently 

 in the bud). 



The true generation has only been known at a very recent 

 period. The first observation upon this subject, which, however, 



♦ Bull. Acad, de St. Petersb., 1855, p. 297- 



t In Miiller's Archiv for 1854, p. 205, A. Schneider describes a mode of 

 propagation in Difflugia Enehelys as sprouting or gemmation, which, never- 

 theless, is perhaps more properly to be regarded as fissation. Stein also 

 describes (p. 191) a propagation by formation of buds in Uvella bodo, 

 Ehrbg. ^ Phacelomonas bodo, Stein. 



