APPENDIX D. cvii 



a few days by a Kolpoda ; afterwards large Euploles with 

 prominent green globules, probably a new species ; and 

 lastly, colourless specimens of Euplotes charon, exhibited 

 themselves, all the species following each other in suc- 

 cession in the course of three weeks, a new form appearing 

 on the decline of a preceding, attaining its maximum in 

 number, and then decreasing in its turn to make room for 

 the next in the series.' 



But can we even say that the developmental cycle is con- 

 fined to Amoeboid and Infusorial forms ? Very much un- 

 certainty undoubtedly exists on this subject, and the state- 

 ments of Agassiz, Gros, and others, however incredible they 

 may appear, should, we think, be kept in view as possibilities, 

 rather than summarily rejected on account of any a priori 

 considerations. Agassiz maintains that the Ciliated Infusoria 

 have no title to exist as a distinct class. ' Most of them,' he 

 says \ ' far from being perfect animals, are only germs in an 

 early stage of development. The family of the Vorticellce 

 exhibits so close a relation with Bryozoa, and especially with 

 the genus Pedicellina, that I have no doubt, that wherever 

 Bryozoa should be placed, Vorticella should follow and 

 be ranked in the same division with them. The last 

 group of Infusoria Bursaria, Paramecium, and the like 

 are, as I have satisfied myself by direct investigation, germs of 

 fresh-water worms, some of which I have seen hatched from 

 eggs of Planaria laid under my eyes V 



But even if such observations are perfectly correct and true, 

 the evolution of a Ciliated Infusorium, out of the egg of a 

 Planaria, would by no means necessarily carry with it the 

 counter proposition, that such Ciliated Infusoria were them- 



1 ' Ann. of Nat. Hist.,' 1850, vol. vi. p. 156. 



2 Mr. Girard confirms these statements, and maintains that Kolpoda 

 cucullus is one of the embryonic stages of fresh-water Planaria. 

 1 Proceed, of American Associat.,' 1848, p. 402. 



