0¥ THE PROTOZOA. CILIATA. 363 



having sheaths betwixt ■^"' and -^"' in length ; those most common were 

 from ^ij'" to ^"' in length and J-g-'" in width. The height of the cap- 

 sule of the Acineta was from -^"' to -^"', and its width not much less. 

 Moreover, intennediate phases between Vaginicola and Acinetina were met 

 with, — as, for instance, capsules occupied anteriorly by the contracted body, 

 which still exhibited, upon being moved up from the bottom of the case, 

 the posterior annular furrow and traces of the ciliary wreath previously 

 existing, and had its anterior half enveloped in a gelatinous lamina, uniting 

 it to the inner surface of the sheath, which was at one time more, at another 

 less, incui'ved upon the animal, but had as yet not been converted into the 

 peculiar pent-house-like cover. 



The metamorphosis, therefore, of a Vaginicola into an Acineta may be 

 thus explained. The animacule is in the fii'st place contracted in the ordi- 

 nary manner ; it then developes its posterior fiuTow and ciliaiy wreath 

 (XXYII. 11), and, detaching itself from the bottom of its sheath, rises to the 

 upper part, which it entii^ely fills and closes up. From this time the rotary 

 apparatus and digestive tube dLsappear by absorption ; the excretion of the 

 gelatinous matter from the fore part ensues, and fixes the animal in its posi- 

 tion, while its tendency to fall to the bottom of the case, and to contract, 

 draws inwards the mouth of the case, and completes its enclosure within a 

 shut sac or capsule (XXYII. 12). The contractile tendency of the body 

 still continuing to operate, brings about a narro^^ing of the anterior part, 

 and with this a consequent elongation of the sheath ; in this way an ex- 

 planation may be given of the veiy long specimens frequently encomitered. 

 The extrusion of the tentacles is an after-occiu-rence (XXYII. 13). 



The complete Acineta can entangle smaU Infusoria with its tentacula, 

 which, by their crossing and retraction, draw the captured particles to the 

 siuface, where probably their nutritive matters are absorbed through it; 

 at aU events, no food or foreign particles are seen in the interior. 



Stein next attempts the identification of this Acineta of Vaginicola crystal- 

 Una with the Acineta mystacina of Ehrenberg, and in a subsequent paj)er 

 proceeds to show that it developes within itself a ciliated embryo. Amid 

 many Acinetce, he discovered some bearing a clear oval or roimded cyst, or, 

 less commonly, several such, upon the surface of the enclosing Hd ; where there 

 Avas a plm-ality, they were evidently in difi'erent stages of development. The 

 cyst contained a sharply-defined Infusorial being, of a homogeneous finely- 

 granular substance, and having an actively-pulsating sac. At first Stein 

 imagined these might be animalcules casually afiixed to the Acineta? ; but fur- 

 ther obsei-vation proved their organic connexion with, and derivation from it. 



The cyst-walls were internally soft and gelatinous, and their substance 

 continuous, through the fissm-es of the cover, with the gelatinous layer of the 

 Acineta, of w^hich they might be more correctly represented pouches or 

 diverticula. The appended animalcule is not a bud produced from the 

 Acineta-hodj ; for it is never found in organic connexion with it, but un- 

 doubtedly has its origin as a germ within it, and makes its way outwards. 

 In fact, it is developed from the rounded nucleus by its elongation and sub- 

 sequent transverse fission. The yoimgest cysts are round or shortly oval, 

 and have no other indication of life and movement than that exhibited by the 

 contractile space. In the next stage they are sHghtly emarginate at one 

 end and stiU motionless, whilst in the oldest the fissure or emargination 

 extends deeply into the interior in a curved manner, and veiy clearly exhibits 

 a number of vibratile cilia. In this mature state they enjoy considerable 

 locomotive powers within their capsule, and recall in their form that of con- 

 tracted Vorticelliaa. Thus, at their fore part they present a rounded ciliated 



