Characteristics of Rotifers. 281 



CHARACTERISTICS OF ROTIFERS. 



BY HENBY J. SLACK,, tf.G.S.j HON. SEC. E.M.S. 



{With a Plate.) 



The following paper contains the substance of a lecture 

 delivered by the writer before the Old Change Microscopical 

 Society on the 18th October, and is intended to serve as an 

 introduction to the study of a group of small animals, which 

 from their variety and . beauty have always been favourite 

 objects with microscopists of all grades, from young beginners 

 to profound students of natural forms. 



We may begin by asking, What is a rotifer ? And the 

 answer to this inquiry is rendered somewhat difficult by the 

 important differences exhibited by different members of the 

 group of beings usually designated by the term. If a botanist 

 were asked, What is a chrysanthemum, or " golden flower V 

 he would enumerate a number of qualities amongst which the 

 colour indicated by the name would not be found, because it 

 belongs to individuals and not to the entire group. In like 

 manner a rotifer, or " wheel-bearer," may be a creature which 

 does not exhibit the least semblance of wheels or organs pre- 

 senting an appearance of rotation, and a considerable number 

 of so-called Rotifera only retain the name because it has become 

 a popular one. and because they possess other organs and 

 structure more or less closely resembling those of the common 

 rotifer, from whose aspect the whole group was designated. 



Formerly, rotifers were spoken of as Infusoria, but Ehren- 

 berg distinctly pointed out the superiority of their organization, 

 and observed a great number of important facts concerning 

 their structure and modes of life. In dealing with this, as 

 with other groups, Ehrenberg no doubt made many mistakes, 

 some arising from erroneous interpretations of what he did see, 

 and others resulting from the imperfect instruments at his 

 command, but it is unfair to notice the errors of this distin- 

 guished microscopist without remembering with gratitude the 

 enormous amount of his labours, and the success that has 

 attended a great portion of his investigations. 



Returning to the question, What is arotifer? let us endeavour 

 to obtain a reply by bringing together certain facts pertaining 

 to the wheel-bearing group. Rotifers, then, are symmetrical 

 animals, in which a dorsal and ventral, or back and front sides 

 can be distinguished.* They have a flexible, strong skin, and 



* Mr. Gosse says, " the dorsal aspect is always determined by the eye or eyes 

 being turned towards that surface, by the stomach and intestine passing down it, 

 and by the cloaca being on that side of the foot. The yentral aspect has the 

 manducatory apparatus and the ovary." 



