Voriicellina.} infusobial ANiMAicrrLES. 527 



During the passag'c of food tlirougli this gullet, it is seen to adii])t 

 itself to its calibre, by assuming an elongated or cylindrical form ; 

 but when it aiTives at its open extremity, it assumes a globular figure, 

 and is detached in the general homogeneous mass of the animal, as a 

 fi'ee globule or vesicle, forming what Ehrenberg described as a 

 stomach-sac. Besides the alimentary tube and globules, there are 

 also seen, scattered, vai-iable granules (ova, Ehr.) a contractile sac 

 (seminal vesicle, Ehr.) and a ribbon or band- shaped, curved, and 

 rather opaque body, — the testes, Ehr. — ^but which Stein calls the 

 nucleus. (P. 22, f. 2.) 



The commonly observed modes of propagation of the Vorticellcc, 

 are self-division (fission) and gemmation ; the latter the less frequent. 

 "When fission is about to proceed, the Vorticella contracts its body 

 into a globular shape, di-aws its ciliated front within the body, wliilst 

 the nucleus assumes a transverse position, and an increase in the 

 breadth of the animal proceeds. Division commences at the fore- 

 part of the body, but also soon evidences itself posteriorlj^ ; the 

 nucleus in the mean while shows in itself signs of division, wliich 

 increase, and ultimately the nucleus becomes lili;e the body, divided 

 in half. During this process, the fine granules of the interior dis- 

 appear ; a semilunar cavity is hollowed out at the anterior conical 

 extremity (P. 22, f. 3) of each segment, -with slowly vibrating cilia 

 on its convex edge ; this cavity is the rudiment of the future frontal 

 wreath, into which it finally expands by being opened up anteriorly 

 by a fissure. - 



When fission is complete, the ajipearance is that of two contracted 

 VorticeUse, seated on the same stem, and often placed at nearly right 

 angles with one another (P. 22, f. 4.) The newly developed being 

 further presents a furrow near its base, occupied by cilia ; and by its 

 movements, presently detaches itself from its fellow, and swims 

 abroad freely, but with the previously hinder end forwards, the pos- 

 terior wreath of cilia now forming its organ of locomotion. By and 

 bye the new being comes to a stand still, fij^es itself, pushes out a 

 Btem (P. 22, f. 2) the posterior fuiTOw and cilia then vanish, wliilst 

 the common frontal wi'eath unfolds itself. These phenomena are 

 briefly referred to in a preceding page, 520. 



Propagation by gemmation takes place from one side of the base of 



