OF THE PROTOZOA. CILIATA. 361 



the walls. With this interpretation, however, he was not satisfied ; and at 

 the same time his attention was aroused to the circumstance of Vorticellce 

 occurring so frequently in company with Actinophrys and Podophrya, and to 

 that of the increase in the number of the one as that of the other decreased. 

 He therefore applied himself to watch the changes going on in the cysts de- 

 scribed, and at length satisfied himself of the intermediate changes in their 

 transition into Actinoplirys or Podojphrya — two varieties of the same animal- 

 cide, in his opinion, and not two genera, as usually represented. Stein was 

 brought to the conclusion that this transition takes place, by comparing Podo- 

 phryie at an early stage of development with metamorphosed Vorticella-ejsts. 

 AmoTigPodophryce of the common form, examples occurred ha\dng their usually 

 wide rounded capsule produced into a hollow funnel-shaped pedicle, and thrown 

 into annular folds, alternating with acute, parallel, angular ridges (XXIII. 

 3). Most of these indi\iduals were unarmed ; but some had numerous capi- 

 tate tentacles. On the other hand, old Vorticella-cysts were found in which the 

 enclosed animal had detached itself from the cyst-wall, and become thrown into 

 sinuosities and elevations, the latter of which pressed against the wall, threat- 

 ening to rupture it. These and the above-described Podophryce Stein supposed 

 to merge into one another. The leading changes noticed in the encysted 

 Vorticellce consisted in the disappearance of the nucleus, in the multiplication 

 of the contractile spaces, and in the detachment of the contents from the 

 walls of the cyst (which they.no longer completely fiUed), and their disposi- 

 tion into irregular and changing lobes. Thus far, in detecting such Vortlcella- 

 cysts. Stein proceeds by direct observation ; but his next step is simply h}"po- 

 thesis, viz. suj)posing their contents to shoot out tentacula through the dense 

 capsule, and assume the figm-e of Actinophrys or of Podophrya (XXIII. 1, 2, 

 4, 18, 19). That the metamorphosis should at one time be into the one ge- 

 neric fornix at another into the other, he endeavours to explain by assuming 

 that where no resistance is offered on any side to the developing Actino- 

 phrj^an, it assumes the form of an Actinophrys, but where resistance occurs 

 at one point, it there developes a stem and becomes a Podophrya. To coun- 

 tenance his hypothesis further, he appeals to the great similarity between 

 the Acifieke met with in company with Vorticella nehidlfera on duck-weed, 

 and Podophi-yce — so great, he says, that when the former are detached, it is 

 difficult to know them from Podophryce. 



Granting that the history of metamorphosis is thus far complete and 

 satisfactory, it remains to show what becomes of the Actinophryans thus 

 transformed from the cysts of Vorticellce, and to reply to the question whe- 

 ther they originate a generative act, At the outset of this inquiry Stein 

 finds himself at variance mth KoUiker and others respecting the structure 

 and vital endowments of Actinophrys. The writers referred to state Acti- 

 twphrys to receive food within its interior, to excrete undigested matters, and 

 to exhibit certain powers of locomotion ; these peculiarities Stein ignores,. and 

 insists on identifjdng the Acinetiform beings he has encountered with Actino- 

 phrys Sol and Podophryafixa, which, he affirms, give birth to a ciliated embryo. 



This embryo, he asserts, is produced within a defined cavity, so far larger 

 than itself that it can move mthin it (XXIII. 2, 4, 5). Its figure is pear- 

 shaped mth a central constriction, and several folds occupied by cilia ; and 

 it ajDpears composed of a finely-punctate sarcode, containing, in the axis of 

 its posterior and larger segment, an oval or band-like nucleus, and near 

 to this a circular actively-pulsating space, and occasionally, on the other 

 side of the nucleus, a second smaller one. No mouth could be detected. 

 The being, as a whole, very closely resembles a detached gemma of Vorticella 

 microstoma, into which it can be very easily conceived to be changed, on fix- 



