4 THE ROTIFERA. 



flower. What happens to them tliorc we cannot see ; for round the stem is raised a tube 

 of golden-brown balls, all regularly piled on each other. Some creature dashes by, and 

 like a (lash the flower vanishes within its tube. 



We sink still lower, and now sec on the bottom slow-gliding lumps of jelly that 

 thrust a shapeless arm out where they will, and, grasping their prey with these chance 

 limbs, wrap themselves round their food to get a meal ; for they creep without feet, 

 seize without hands, cat without mouths, and digest without stomachs. 



Time and space, however, would fail mc to toll of all the marvels of the world 

 beneath the waters. They would sound like the wild fancies of a child's fairy tale, and 

 yet they are all literally true ; and, moreover, nearly all of them are true of that roti- 

 ferous world which it is my purpose to describe. 



]5ut it will be natiually asked by those of my readers to whom the subject is new, 

 " What is a Hotiferon ? " and no doubt one would say that a book about Eotifera ought to 

 begin at tlie beginning, and define precisely what a Kotiforon is. 



Precise definition is, however, in such a case, quite out of the question ; for, though it 

 is easy enough to dofhic the typical form of a natural group of animals, or even to 

 include in the definition forms that must be placed not far off from the central one, yet 

 in the ambitious attempt to frame a definition that shall include many families, we find 

 (as we get farther away from the typical form) that one by one all the positive statements 

 are disappeai'iug from our definition ; and at last we have nothing left but the mere 

 shell of a proposition, with everything worth the stating struck out of it. 



The llotifcra, then, are small aquatic animals varying from ^ to ^l^j of an inch in 

 length, and deriving their name from a wheel-like appearance produced by fine circlets 

 of hairs seated on the front of their heads. A few species are marine ; but the great 

 majority known to us belong to fresh water, and are to be found in ditches, ponds, reser- 

 voirs, lakes, and slowly running streams, sometimes attached to the leaves and stems of 

 water plants, sometimes creeping on the alga;, sometimes swimming freely through the 

 water. Altliough the greater number of the genera resemble each other in the chief 

 features of their internal organization, so as to form a very natural group of animals, yet 

 there are several aberrant forms which would render it a difficult matter to include them 

 all in one precise definition. 



This indeed could be done only by introducing so many qualifications and exceptions 

 to every statement, that the portrait would be rendered too vague for any reader but one 

 already familiar with the whole subject. 



Of tlie greater number, however, it is enough to say : 



(1) That they swim by means of hairs on the front of their heads. 



(2) That they possess a simple stomach and intestine ; and peculiar jaws. 



(3) That they have muscles which are sometimes striated, and which often pass 

 freely through the cavity of the body. 



(•1) Tliat they have a well-developed vascular system. 



(5) That their nervous system consists of one ganglion, with nerve threads radiating 

 to their organs of sense. 



(0) That they are dioecious; have ova of two kinds ; and do not pass through any 

 distinct metamorphosis. 



Thougli the above six statements are precise enough, aiul in the main true, yet it 

 will l)e as weM for tliosc, who are not versed in the subject, to pass them over for the 

 present, and first to master the structure of some one typical Rotiferou ; as, when this has 

 been done, the general conception of a Rotiferon will be easily grasped, and the variations 

 from the type readily followed and understood. 



For this purpose I have selected Bracliiomts ruhcns, whose figure is given much 

 magnified in I'l. A, fig. 1. The genus Brachiomis is to be met with almost every- 

 wliero. It is hardly possible in summer to take a dip of water from a garden-pond, or 

 to gather the alga) from its walls, without bringing up some specimen of the genus. 

 Brachiomis rubcns is a fairly common species. It is comparatively a large handsome 



