501 



"Auch eine Bemerkung von Kraft (Zur Physiologie des Flimmer- 

 epithels bei Wirbeltieren, Pflügers Archiv, Bd. 47, 1890) über das 

 'Zucken des Flimmerepithels' (Rachenschleirahaut des Frosches) ge- 

 hört wohl hierher. Nach seiner Beschreibung sieht man an den be- 

 treffenden Stellen (1. c. p. 230) 'ein wogendes Hin- und Hergehen 

 oder eine ruckartige Bewegung großer Flächen, einem Zucken eines 

 sich mäßig schnell zusammenziehenden Muskels vergleichbar'. Daß es 

 sich bei diesem Phänomen nicht um die Zuckung unterliegender 

 Muskeln handelte, konnte Kraft an losgelösten Zellreihen zeigen, die 

 auch isoliert noch die Erscheinung darboten." 



If these observations (which, it may be noted, all belong to Me- 

 tazoa) are correct, the activity of the cilia is accompanied and in all 

 probability caused by movements in the cell-protoplasm. 



It would at first sight appear that, if it be the case (and there 

 seems to be no doubt of the fact as regards the cilia of some 

 Protista and, according to Meves, as regards the tail of the 

 Salamander spermatozoon) that ciha completely isolated from every 

 part of the cell-body can still for a time continue to execute rhythmic 

 movements^), any theory which is based upon their movements being 

 produced by activity of the cell- protoplasm must fall to the ground. 

 This seems indeed to have furnished Dr. Pütter with his chief reason 

 for rejecting such an idea. But a little consideration will shew that 

 this is by no means necessary so far as concerns the vast majority 

 of cilia. Very few cilia possess the faculty of independent motion 

 when severed from the cell-body and most if not all cilia in animals 

 higher than Protozoa have a regular constant mode of action and do 

 not exhibit the variations which are seen in some Protista. This 

 difference between the mode of action of cilia in the lowest and in 

 higher organisms is not difficult of explanation, for it is manifestly the 

 result of evolution, with consequent diff'erentiation of function. This 

 is easily to be understood if we consider the mode of development of 

 cilia, which is thus described by Dr. Pütter (p. 101): "Die Ent- 

 wickelung der Cilia scheint sich fast ausschließlich in der Weise zu 

 vollziehen, daß ein Fortsatz einfach aus dem Plasmakörper der Zelle 

 hervorwächst". 



p. 69: "Bei Protozoen kennen wir im wesentlichen zwei Modi, 

 wie 'Cilien' entstehen können. Der häufigste scheint der zu sein, 

 daß sich eine kleine Emergenz hyalinen Plasmas erhebt, die sogleich 



1) Several instances are given by Dr. Pütter (p. 39 et sequ.) but 

 it is not necessary to quote the passages at length. 



