476 . Dr. A. Graber on the 



transversely (fig. 1, p. 493) , whilst with sections in the longitu- 

 dinal line the two halves^ which of course are long and narrow^ 

 usually become rolled up, and the regenerated parts often 

 appear crippled at first, a peculiarity which, however, as 

 already remarked, usually disappears subsequently. We may 

 therefore say of Stentor, as of Oxytriclia^ that the anterior end 

 replaces the lost posterior end, and the right side the lost left 

 side, and vice versa. 



The question now is, in what manner does this regeneration 

 take place ? and for the settlement of this question Stentor is 

 perhaps the best of all Infusoria. Let us first of all consider the 

 anterior part of a Stentor separated by a transverse cut; it is at 

 first broadly truncated at the cut surface (fig. 1), but gradually 

 the body becomes drawn out in length posteriorly, the streaks 

 taper off, and in this way the well-known tapering posterior 

 end is again developed, in which the body-parenchyma pro- 

 trudes as an apparatus of adhesion. In this mode of regene- 

 ration it would almost appear as if no new formation of parts 

 occurred, but rather only a change of position of those already 

 present. Of course the process of regeneration is much more 

 complicated in those specimens of which the anterior end has 

 been cut away transversely. In these also we have at first 

 a straight line or flat surface at the point of section : in time, 

 however, the body of the fragment becomes rounded off at its 

 anterior end until it has again acquired a clavate form ; but 

 it is still destitute of any of the large cilia, as indeed the 

 whole peristomial area, with the mouth and the spiral of cilia, 

 has been removed. The reproduction of these lost organula 

 actually takes place in exactly the same way as in spontaneous 

 division. The latter process, as is well known, commences 

 by the formation in the median line of the dividing Stentor 

 of a vertically placed stria of large peristomial cilia (membra- 

 nellse), and as the process goes on the more does this line of 

 cilia grow, gradually bending into an arc, until finally it 

 forms a circlet of cilia, which constricts off the so-called peri- 

 stomial area from the rest of the body. At the same time one 

 end (the right) of the stria sinks spirally into the interior of 

 the body, and thus forms the mouth and the oesophageal 

 funnel. In the " decapitated " Stentor also the new peristo- 

 mial cilia make their appearance on one side, arranged in a 

 vertical line (fig. 2), which then during the further growth 

 surrounds the anterior extremity and originates the peristo- 

 mial area and the mouth. Here, therefore, we have the 

 interesting tact that the regeneration of the organula in the 

 Infusoria follows the same course as their new-formation in 

 spontaneous fission. The to us unknown impulse which 



