Natural History of the YoYticcWse. Ill 



forms, namely : — the Astylozoon described by Engelmann, 

 which rejoices in constant spontaneous mobility, but at the 

 same time possesses two springing-set^e {Schnellborsten) at the 

 hinder end of the body, perhaps as the homologue of the pe- 

 duncle ; and, further, the genera Scyphidia and Gerda^ which 

 are, indeed, completely non-pedunculate, but are more or less 

 sessile. But if we examine the peduncle of the VorticeUce, 

 especially in comparison with the peduncle and envelope of 

 the Ophrydina, we cannot reject out of hand the intimate 

 correlation of these structures. The peduncle of the VorticeUce 

 consists of a hyaline homogeneous exterior envelope or sheath 

 and a darker, more or less granular axis. The latter is either 

 muscular substance*, and in this case, with the whole pedun- 

 cle, retractile (VorticeUa, Carchesium, &c,), or the axis con- 

 tains no muscular elements, and then the peduncle is rigid 

 (Ejyistyh's) . But in both cases the exterior hyaline envelope 

 of the peduncle embraces the hinder basis of the body of the 

 animal, whilst the axis alone penetrates into this base, be- 

 coming amalgamated with it, and here either serves merely 

 for the attachment of the animal and of the retractor muscular 

 elements in it [EjnstyUs), or, when the axis itself is of a mus- 

 cular nature, radiates out continuously in the body ( Vorticella, 

 Carchesium). Now in the Ophrydina in general both the 

 envelope and the body of the animal are likewise attached by 

 a peduncle, although this is usually very short ; and yet this 

 may be regarded as morphologically equivalent to the peduncle 

 of the VorticeUce, and, indeed, especially to that of Ejn'stylis. 

 The sheath which in the Vorticeike envelopes the axis of the 

 peduncle, and terminates at the hindmost base of the body of 

 the animal, is continued forward beyond this base in the 

 Ophrydina, rising into a wide beaker-shaped case, within 

 which the whole animal can retract itself. But even the axis 

 of the Vorticellan peduncle is not wanting in the Ophrydina, 

 but it is what, just as in the VorticeUce, enters the base of the 

 body and effects the attachment. Thus the more accurate in- 

 vestigation of the constitution and secretion or development of 

 these structures may only render their identity still more clear. 

 From all this it seems to me more natural to accept the indi- 

 vidual genera of the Ophrydina as members of the Vorticellan 

 family than to separate them from the latter. 



Stein has furtlier placed the family of the Vorticellina 



* We retain here the denomination "axis " for the sake of uniformity, 

 even for the contractile peduncles, although, as is well known, in Vorti- 

 ctlhi and Carchesium the muscular cord has a spiral course round the axis 

 within the sheath, and only occupies a position in accordance with the 

 true axis in Zoothamniinn. 



