On the Morphology and Physiology of the Cell. 209 



I am very strongly of the opinion that the same meta- 

 morphosis or degeneration from the ciliated to the amceboid 

 state is of great importance in the histology of inverte- 

 brates. Not only does it frequently take place among 

 ciliated embryos, but the amoeboid corpuscles of many in- 

 vertebrates {e.g. Echinus) develop in the same way from the 

 ciliated epithelium of the perivisceral cavity.* So, too, I 

 have elsewhere f described the remarkable transformation 

 which occasionally takes place (doubtless as a pathological 

 change) in the ciliated ectoderm of a planarian ; and it is 

 here possible to watch the actual transformation of cilia 

 into pseudopodia, and even to see the two slowly contract- 

 ing together. May not the assumption of this change with 

 diminishing vitality throw light upon diseases of the ciliated 

 epithelium of the trachea ? 



Chun has recently shown that, as had often been sur- 

 mised, the vibratile bands of Ctenophores are simply united 

 cilia, for when macerated they separate. 



8. While the principal forms of contractile tissue are, of 

 course, the muscular, the ciliated, and the amoeboid, it is by 

 no means correct to suppose that no other forms are known. 

 The remarkable contractile collar of Torquatella,X the heart of 

 Appendicularia,§ the extraordinary infusorian Pulsatella}\ 

 which moves by the rapid rhythmical contraction of internal 

 fibrillae around the large vacuole, are instances of new and 

 strange modes of contractility ; while the spermatozoa of 

 Urodeles, which are provided with an undulating mem- 

 brane along one side, or those of certain planarians,!! where 

 a regular series of waves runs continuously from one end 

 of the spermatozoon to the other, increasing in velocity, 

 though not in amplitude, towards the end which bears the 

 flagellum, are, if possible, even more valuable as illustrations 



* Op. cit, Arch. d. ZooL, Exp., 18S0. 



+ Op. dt., Proc. Ro3^ Soc. Lond., 1879. 



X Lankester, Torquatella typica (Quart. Jour. Micro. Sci., vol. xiv., \%1\). 



§ Lankester, On the Heart of Appendicularia (Quart. Jour. j\licro. Sci., 

 vol. xiv., 1874). 



II Sur une nouvelle sous-classe d'Infusoires (Comptes Rendus, 19tli Dec. 

 1881). 



^ Geddes, On the Histology of Convohita (Proc. Roy. Soc. Lond., 1879). 

 VOL. VII. ' 



