362 GENEKAL HlSTOKY OE THE INFUSORIA. 



ing itself by its anterior end and then developing, in its larger and hitherto 

 posterior segment, a mouth and ciliary 's\Teath. 



After Hvely rotary movements -within what might be called its uterine 

 cavity, the embiyo escapes with a sudden bound, and gains a fi'ee, active 

 existence. The passage by which it has made its way thi^ough the substance 

 of the parent Actinophrys continues for some time open, but is gradually 

 closed up from behind. The size of the embryo is proportioned to that 

 of the parent, and varies between jj-^'" and -^"'. The diameter of the 

 smallest parent being in which a matiu^e germ presented itself, scarcely 

 exceeded -J3-". 



One other instance "will suffice to illustrate Stein's hypothesis of Acineti- 

 form transformation. The one we select is the Vaginicola cri/staUina, which 

 that author attempts to show becomes, by a metamorphosis, Acineta mystacina 

 (XXYII. 10-15). Out of a large number of specimens contained in a 

 vessel of water, few could be found at the end of foiu'teen days, the place 

 of the great majority ha\dng been assimied by Acinetina. This occurred 

 even when great pains were taken to isolate a certain number of Conferva - 

 filaments richly covered ^vith Vaglnicolce, and to place them in pui'e spring- 

 water, so as to avoid the introduction of other colonists. That the Aciiietce 

 were derived from the Vaglnicolce, a comparison of the structure of the two 

 will indicate. The contracted body of the Vaginicola may be recognized in 

 the Acineta detached from the bottom of its sheath and raised to the upper 

 pari, which it completely fills, — the mouth of the sheath having previously 

 been bent inwards over it as a cover, and a layer of gelatinous matter poured 

 out to bind the two together. The outermost parts of the roof-like cover 

 project freely above tliis layer, and are traversed by several radiating folds or 

 fissures. The clearest notion of the transformation efi'ected is obtained when 

 we can look down upon the top suriace of the capsule, by getting the axis 

 perpendicular to the eye. 



The contained body is closed in on all sides ; and its contents are substan- 

 tially the same as those of the body of the Vaginicola (XXYII. 12), with 

 numberless fine granules, and sometimes with a preponderating number of 

 large granules scattered through them, rendering the body opaque and of a 

 greyish-yellow coloiu-. There is likewise a similar roimd contractile space ; 

 but instead of a band-Hke nucleus, there is a rounded one. This diff'erence 

 in respect of the nucleus is not important, inasmuch as its length varies 

 greatly in Vaginicola according as the animal is extended or in a contracted 

 state, — being in the latter much shortened or merely elongated- oval, whilst 

 in the former its length exceeds two or three times its width. Hence it is m 

 no way remarkable that, in the very contracted condition of the encysted and 

 Acinetiform state, the nucleus should be veiy much shortened and rounded, — 

 a change which analogy, indeed, -with various encysted animals would lead 

 us to anticipate. 



From the upper surface of the encysted body Yeiy many bristle-Hke 

 tentacles with knobbed ends are given off, which penetrate the gelatinous 

 layer through the fissures in the cover of the sheath, and outspread them- 

 selves in a radiating manner. These tentacles are for the most part straight, 

 and slowly extend and retract themselves in length. Pressure causes theii- 

 contraction, and huddles them together ; but they are not entirely withdi-awm. 

 Some smooth Acinetiform specimens are met with, which may be considered 

 to be in an earlier stage, and similar to the incomplete Acineta of Epistylis 

 plicatilis. 



The origin of the Acinetce from Vaginicola is further substantiated by the 

 relative dimensions of the two. Thus Vaginicolce were foimd on Conferva; 



