PEEFACE. 



NEARLY fifty years have passed, since Ehrenberg's successful invasion of the 

 unseen world was made known by the publication of his noble work, Die In- 

 fusionsthierchen ; and twenty-five since Dr. Arlidge's edition of Pritchard's excel- 

 lent History of Infusoria brought together, in a convenient form, the results of 

 the long and patient observation of many investigators. 



Meanwhile memoirs on various species of Eotifera, as well as the number of 

 species themselves, kept slowly increasing ; and, what is of greater moment, 

 the prolonged study of these interesting atoms, by several acute observers, has 

 made clear some of the perplexing difficulties in their structure, and swept away 

 many mistakes both of observation and inference. 



Under these circumstances the authors of this work believed that such a 

 book as the present was much wanted ; and they hoped that their prolonged 

 study of the Eotifera (continued, in the case of each author, almost daily, for 

 upwards of thirty years), as well as their invariable habit of drawing from life 

 all that they had observed, would enable them, by means of their long accumu- 

 lated stores of drawings and notes, to meet this want. 



They venture to think, from the manner in which, so far, the book has been 

 received, that this belief and hope have both been justified ; and in confirmation 

 of the favourable opinions of it that have already been expressed, would point 

 out (they trust with pardonable pride) that this work contains more than 120 

 species which were unrecognized when Dr. Arlidge wrote ; that nearly the whole 

 of these have been added to science by the authors themselves ; that about 

 eighty of these new species, chiefly among the Plo'ima, have been found by one of 

 the authors during the last fifteen months ; and that the other by the discovery, 

 among other remarkable forms, of Pedalion minim, has put beyond question the 

 fact that the ROTJFERA, in one point at least, are closely linked to the ARTHROPODA. 



The thirty coloured plates have been divided nearly equally between the two 

 colleagues ; the small uncoloured plates A, B, C are by Dr. Hudson. The figures 

 in plate D are taken from various sources ; but in every case, both here and in 

 the coloured plates, the original authority has been indicated ; the initials G or 

 H being attached to those figures which have been drawn from the life by Mr. 

 Gosse or Dr. Hudson. Mr. Gosse's independent portions of the text are always 

 inclosed in square brackets [ ], and marked at the end with his initials, P.H.G. : 

 the portions not so marked are by Dr. Hudson, including the first four chapters. 



