Natural History of the Vorticellse. 463 



Sometimes I thouglit I could detect a connexion with the con- 

 tractile reservoir, sometimes, as in the case of the latter, a 

 union with the initial portion of the alimentary tube — that is 

 to say, an opening into it ; but I was unable to arrive at any 

 certain information upon this point, as, indeed, upon the signi- 

 ficance of the whole structure. 



Reproduction and Development of the YorticellEe. 



The asexual reproduction of the Vorticellaj by fission is one 

 of the oldest observations of the kind upon the Infusoria and 

 lower animals in general, and has been confirmed times out of 

 number. In all VorticelljE (if we except the genus Lageno- 

 phrys belonging to the Ophrydinas, which increases, according 

 to Stein, by diagonal fission), it occurs as longitudinal fission, 

 and, indeed, as a division into two more or less completely 

 similar halves. The introduction to fission is always that the 

 Vorticella retracts the ciliated organ into its interior, con- 

 tracts the peristome firmly over it, and remains in this con- 

 tracted, spherical condition for some time, during which the 

 contractile-stalked forms repeatedly spring back. Soon after 

 this the spherical form is seen to become flattened from before 

 backwards, whilst the lateral parts gain in extension (PI. XII. 

 fig. 1). At the same time the cord-like nucleus places itself 

 transversely — probably, in the first place, because the whole 

 body is drawn out to the right and left ; and the contractile 

 reservoir is also driven to the median longitudinal axis 

 (PI. XII. figs. 2 & 8). Now the constriction commences. 

 First of all we see a slight depression make its appearance in 

 the middle of the anterior surface of the body (PI. XII. fig. 1) ; 

 and this is soon followed by an emargination on the posterior 

 base of the body attached to the peduncle. The two con- 

 strictions, occupying the two longitudinal poles of the body, 

 advance towards each other, so that the whole body is soon 

 surrounded by a median longitudinal annular furrow, which 

 in the first place divides the surface into two equal lateral 

 halves (PI. XII. figs. 2 & 8). This annular furrow cuts in 

 deeper and deeper, whilst the jerking back by means of the 

 peduncular muscle is more frequently repeated, by which the 

 contractions and the whole process of constriction are evi- 

 dently forwarded. The nucleus, the contractile reservoir, the 

 ciliated organ, and the peristome are drawn in to take part in 

 the act of fission ; and finally, when the two halves are com- 

 pletely separated, and only connected at their base by the 

 peduncle, each fissional scion has almost completely the organi- 

 zation of the parent animal, and does not even differ greatly 



