OF THE PEOTOZOA. CILIATA. 349 



orifice of the sheath, whilst the posterior lies immediately behind it, fixed from 

 want of space, and unable to free itself (XXX. 36). The question that now 

 presents itself is, how is the newly-formed animal to escape its prison and 

 to exercise its vital endowments ? This, Stein has been able to solve by ob- 

 servation of another species of Lagenoplirys, viz. L. Amjpidla. The upper seg- 

 ment ceases to put forth its ciliary organs and to take in food, and shortly 

 contracts itself and detaches its hold from the opening of the external sheath, 

 developing simultaneously a row of cilia around its margin (XXX. 35). It 

 also not unfrequently happens that the body is divided from the peiistom, 

 leaving this portion adherent in its natural position to the orifice of the 

 sheath, and possessed of such remarkable vitality, that it continues to con- 

 tract and dilate, and to implicate the orifice of the sheath itself in its move- 

 ments (XXX. 35). AVhen the peristom, with a portion of contractile sarcode 

 (35 I) enclosing at times a contractile space within it, thus plugs the 

 only outlet from the cyst, the two products of fission cannot gain their 

 liberty, and only enjoy the limited degree of locomotion allowed within theii- 

 narrow prison-house. But where, as is more common, the orifice is opened, 

 they sooner or later make their way out, experiencing, nevertheless, some 

 difficulty in passing through the narrow outlet. 



A curious circumstance pertains to these fission-products of Lagenophrys, 

 and indeed to those of all the OpTirydlna and Vorticellina, viz. they are not 

 precisely like the parent. Thus, the young of Lagenoplirys, produced as 

 above described, exhibit the rotary organ and peristom in a contracted con- 

 dition, whilst a row of ciHa surrounds the body in a ring-Hke groove on the 

 abdominal siuface, and serves the purpose of a locomotive organ (XXX. 35, 

 36). On the ventral aspect, adds Stein, the figui'e of the animalcule recalls 

 that of Stylonychia, between w^hich and the normal form of Vorticellina it 

 may be considered a transitional type. 



Turning now to the other members of the Vorticellina and Ophrydina, we 

 see that the history of the fission-products differs according to their habits 

 and structural peculiarities. In the branching forms many of the newly - 

 formed beings proceed each to secrete from its base a pedicle, and so continue 

 the dichotomy of the little arborescent colony they belong to. Others, on 

 the contrary, detach themselves from the parent-stem and enter on a free and 

 independent existence. In this case one of the two segments consequent on 

 self-division, in order to enter on its new mode of Hfe, undergoes certain 

 modifications in structure, viz. it continues in a completely contracted state, 

 and a furrow appears about the posterior third of the body, within which a 

 ciliary circlet develops as the locomotive organ of the animal (XXVII. 11). 

 This occurrence is general among Vorticellce and Ophrydina ; for among the 

 former the pedicle never ramifies, and in the latter one fission -product must 

 quit the capsule, which serves as the nidus of only one being at a time. 



The after-history of these locomotive segments is widely different in dif- 

 ferent specimens. Some, after swimming about for a time, come to a state 

 of rest, affix themselves by theii' posterior extremity, and produce, according 

 to their natural habit, either a stalk or a sheath, and resume aU the charac- 

 teristics of the parent-stock. Others, again, become quiescent, but instead of se- 

 creting a pedicle or sheath, proceed to encyst themselves, either for their own 

 preservation or preparatory to the fulfilment of an act of reproduction. In- 

 deed, the process of encysting may overtake the animals whilst still seated 

 on their stalk or within their case, and thus anticipate the formation of the 

 posterior ciliary wi-eath. 



Lastly, in a few genera, fission seems only, or at least mostly, to occur 

 after the animalcules are encysted. Stein represents this to be the case ge- 



