352 GENERAL HISTORY OF THE INFUSORIA. 



Speaking of this process in Vorticellce, Stein (ojy. clt. p. 28) says, the interior 

 of the knob-like process is quite homogeneous at first (XXVII. 1) ; but when 

 it has attained a hemispherical shape, a crescentic cavity forms at its anterior 

 part, from which the peristom, rotary organ, and alimentary tube are even- 

 tually developed (XXX. 17, 27), just as happens in the result of fission. 

 Whilst this proceeds, the swelling acquii^es an oval or globose figure, and 

 the width of its attached base d^vindIes to a constricted neck or isthmus. 

 The addition of acetic acid proves that no portion of the nucleus extends into 

 it, but that this organ retains its normal cui'\'ed reniform figure. Stein here 

 adds the remark, that no sharp Kne of distinction exists between self-fission 

 and gemmation — that the latter may be looked upon as an act of unequal 

 division, in which the whole organization has to be created, and not, as in 

 fission, simply perpetuated ; or fission may be described as a variety of 

 gemmation, one segment being regarded as a bud ; at least this view holds 

 good in the case of transverse fission. Longitudinal fission consists in the 

 formation of two gemmae, which subsequently involve the entire being. So 

 also in one sense gemmation does not always end in the production of a single 

 bud ; for VorticeUce with two are common, and occasionally with three, one of 

 which is ready for detachment, whilst the other or others are very incomplete. 



In Sp'irochona (XXX. 17, 27), which does not multiply by fission, gem- 

 mation is very frequent ; and often two buds are produced, one immediately 

 behind the other, the hindmost being first in development. Where two 

 exist, the first-fonned usually appears on the side of the body at its widest 

 part ; and the second forms subsequently in front of it, nearer the neck. Re- 

 latively to the size of the parent, the bud is usually of greater dimensions 

 than in VorticeUa, and may, by thrusting aside the head of the Sj;>irochona, 

 place itself in the longitudinal axis of the body. \\Tien the gemma com- 

 mences to contract its base and to acquii^e the form of an independent being, 

 an opaque, sharply-defined, homogeneous speck makes its appearance about 

 its middle, or, rather, in front of it, which, by further development, becomes 

 the nucleus (XXX. 17), wliilst a shallow groove displays itself at its anterior 

 tiTincate end, and somewhat later is transformed into a curved and rather 

 angular ciliated fissui'e extending some way down one side of the body. 



In this so-formed gemma of Spirochona there is, therefore, a wide depar- 

 ture from the rule observed in any of the VorticeUina and Ophrydina. No 

 posterior ciliary wreath is fonned ; and the anterior ciliary apparatus, together 

 with the head itself, is at first developed in a temporary and rudimentary 

 manner. After moving about for some time by means of the ciliary antero- 

 lateral chaimel, the free gemma fixes itself by its posterior extremity, by an 

 adhesive substance, or occasionally by a short stem ; and then the opposite 

 sides of the ciliated furrow approximate, and coalesce behind, whilst in front 

 one edge rises above the other (XXX. 19), and soon forms a spirally-con- 

 voluted membrane, which becomes clothed with cilia replacing those of 

 the old furrow, which are absorbed and disappear (XXX. 20). This growth 

 into perfect Spirochonce does not happen with all gemmae ; for some assume a 

 quiescent condition, become encysted, and, if Stein be right, are ultimately 

 converted into very peculiar Acinetiform beings — the Dench-ocometes para- 

 doxus (XXX. 23). Before encysting, the cilia cease to play, and disappear ; 

 and very soon the furrow itself closes up. When enclosed within the trans- 

 parent but firm capsule, nothing but a finely-granular homogeneous substance 

 appears, containing the peculiar nucleus, which, however, requires the action 

 of acetic acid to display it (XXX. 21). 



The process of gemmation presents several peculiarities in the genus La- 

 genophrys, due mostly to the peculiar connexion between the enclosed ani- 



