INFUSORIA. 115 



free, they lose their crown of cilia, take a cylindrical form, more or 

 less ovoid and elongated, and move themselves by means of a new 

 organ. " There is no animal," says Dujardin, " which excites our 

 admiration in a higher degree than the Vorticellate Infusoria, by 

 their crown of cilia, and by the vortex which it produces ; by their 

 ever-varying forms ; above all, by their pedicle, which is susceptible of 

 rapid spiral contraction, by drawing the body backward and again 

 extending it. This pedicle is a flat membranous band, thicker upon 

 one of its edges than the other, and containing on the thicker side a 

 continuous channel, occupied, at least in part, by a fleshy substance, 

 analogous to that of the interior of the body. During contraction, 

 this thick edge is shortened more than the thin side, and hence results 

 the precise form of the spiral of the corkscrew." 



We cannot conclude our brief history of these curiously-organized 

 beings without recording the doubt which still exists in the minds of 

 our most eminent naturalists, whether some of those we have named 

 are animal or vegetable in their origin. The Desmidese, long classed 

 among animals, are now generally recognized as plants. The group 

 of Diatomacece are still considered doubtful, and the Monads and 

 Volocina are still subjects of discussion, the evidence inclining in 

 favour of those who argue for their vegetable nature. Messrs. Busk, 

 Williamson, and Cohn, have published in the " Microscopical Trans- 

 actions " minute details of the evolutions of these curiously-organized 

 globules, which seem to prove their vegetable nature. On fhe other 

 hand, it is difficult to imagine so accurate an observer as Agassiz 

 writing so positively as he does on a doubtful subject. Eemarking on a 

 former paper, in which he had shown that the .embryo hatched from 

 the egg of a Planaria was a true polygastric animalcule of the genus 

 Paramecium, he adds, that in former writers a link was wanting, viz., 

 tracing the young hatched from the egg of Distoma. " This deficiency," 

 he says, "I can now fill. It is another Infusorium, a genuine 

 Opalina. With such facts before us there is no longer any doubt 

 left respecting the character of all these Polygastria ; they are the 

 earliest larvse condition of worms." Amid these friendly disputes we 

 congratulate ourselves that we have to do with the oceanic creations, 

 both animal and vegetable. 



i 2 



