144 



KNOW^LEDGE 



[March 1, 1886. 



s 1 as to be unintelligible to eacb other, but all can make 

 themselves understood on subjects of general interest. 

 Eich individual does his part to propagate his language, 

 and each generation hands it down by tradition to the 

 next, although in a fi.irm somewhat diiferent from that 

 in which it received it ; but literature, besides having a 

 powerful influence on the language of individuals, as it 

 were stereotyped that of its authors, and is a conserva- 

 tive element in the ever-changing current of human 

 speech. No individual can affect speech except bv 

 setting an example which others follow, for no change in 

 language can take place without the help of the people, 

 and it is thus that each language becomes an index to 

 the average and collective capacity of the community to 

 which it belongs ; for a nation developes language only 

 in relation to its needs. 



PLEASANT HOURS WITH THE MICROSCOPE, 

 By Henry J. Slack, F.G.S., F.R.M.S. 



HE appearance of the first part of a splendid 

 work on " Rotifers," by Dr. Hudson and 

 Mr. Gosse, will excite fresh interest in 

 the study of these wonderful and most 

 ffiscinating objects for the microscope. 

 The new work is necessarily somewhat 

 costly, but, from the beauty and elaborate 

 character of the coloured pl-vtes, it will compare very 

 favourably in point of price with any other first-class 

 monogram. 



Every collector of the minute objects of pond life is 

 sure to meet with some typical species of this interesting 

 family, but many are very local; and although, as the 

 preface to the new work states, upwards of ninety species 

 have been discovered since the last edition of Pritchard's 

 " Infusoria " was publi.shed, twenty-four years ago, it is 

 by no means probable that even the English list of fresh- 

 water kinds is yet completed. 



If the question is asked, "What is a rotifer? ' no 

 simple answer can be given, because the characters of 

 different species vary so greatly and so widely that the 

 details common to all are comparatively few, and often 

 difficult to observe. The earliest and best - known 

 member of the family is the Motif er vulgaris, or Common 

 Rotifer, found not only in ponds, but in gutters, tufts of 

 moss, &c., and able to survive and become reanimated after 

 being dried up and passing an indefinite time in mummy^ 

 like repose. 



The early microscopists were greatly astonished when 

 they saw this creature thrust forth organs which appeared 

 to twirl round on axes, just like watch-wheels. Of course, 

 a little reflection must have led the observer to conclude 

 that this appearance could not exactly conform to reality, 

 but with the imperfect instraments of early date, it must 

 have been very difficult to find out what did actually 

 take place ; and at this day, if a common rotifer is shown 

 to any one ignoi-ant of its nature, the motion of its cilia is 

 pretty sure to draw forth the exclamation that a pair of 

 wheels are spinning round. 



It_ is impossible to understand ciliary motion by ob- 

 serving it in a rapid condition, but any of the larger 

 ciliated creatures common in hay infusions enable it to°be 

 studied and analysed as they become enfeebled, if a 

 water-drop containing them is permitted to get nearly 

 dry. Each cilium then shows its separate motion, which 

 is found to be much like what can be given to a long 

 elastic stick by a brisk movement of the wrist. It is a 

 wave motion from base to tip, and when a number of 



cilia move in rhythmical succession they look like wheels, 

 if they are arranged in a circular pattern, and like ad- 

 vancing waves in an elongated one. 



It is impossible to state how low down in the scale of 

 living things some rudimentary state of consciousness 

 exists, but when we come to the higher rotifers, many of 

 their actions look as if they were guided by intention for 

 a definite purpose, and on one occasion I saw a fight 

 between a Diglena and an Anguillula. The latter seemed 

 to have offended the rotifer by giving it an accidental 

 flick, to which the rotifer responded by thrusting out its 

 mouth and trying to bite the worm to pieces, in which 

 it partially succeeded. I speak of its "mouth," because 

 in this and some other sjiecies the biting organ, commonly 

 called '• a gizzard," can act as an external organ with pro- 

 truding jaws. Generally speaking, the " gizzard " cor- 

 responds more or less with the mouth of insects, as Mr. 

 Gosse showed long ago. 



Ciliary vibration to bring food-particles within reach 

 of a creature's motith may be a very simple business. The 

 currents set up in such cases merely have a general 

 tendency to throw floating particles so that a good many 

 cannot help going through the right way, while, perhaps, 

 the majority are hurled far astray. If, however, the 

 proceedings of a common rotifer are noticed, it will be 

 seen that the actions are much more complicated. The 

 so-called wheels can be moved in various directions, and 

 when their whirlpools have entangled small objects of all 

 descriptions, another set of cilia, exei'ting a selective 

 power, form currents which rapidly take what the 

 creature desires down through the gullet to the so-called 

 gizzard, and thence to the stomach, and reject the rest. 

 When a number of common rotifers, or of other highly- 

 developed free-swimming species, such as the Brachions, 

 are seen near each other in one trough, considerable 

 differences of what would be called skill in more advanced 

 creatures may be frequently noticed, and some might be 

 reckoned much more clever than others in capturing 

 their prey. At any r.ite, they are more successful, but 

 this may happen merely from their being more lively at 

 that particular time, or more hungry. The free-swim- 

 mers have a great advantage over the fixed kinds when 

 their food is at all scarce, and where many are present 

 they often work near each other, as if to gain the 

 benefit of the extensive commotion made by their joint 

 action. This advantage is also gained by the associated 

 colonies of Conochilus. 



The student .should look specially to the character and 

 shape of the ciliary organ of the rotifer he finds. It 

 varies from a complicated pattern in the Common Rotifer 

 and the Brachions (Pitcher Rotifers), to a simple wreath 

 in Limnias, p,nd in some species disappears. lu the 

 Floscules, of which beautiful figures are given in 

 Part I. of the new work, there are no cilia that give 

 an appearance of wheel rotation, but tufts of long hairs 

 which vibrate like the steel notes of a musical-box, 

 without occasioning any strong wave motions. That 

 work is left to less conspicuous organs lower down. 



The chances are that hunting in small ponds where 

 plants are growing, in gutters, amongst bits of leaves and 

 dehris, and especially in duck-ponds, will soon supply the 

 observer with specimens of many characteristic species. 

 The Common Rotifer and the Philodines, which r,re like 

 her, are good swimmer.? by means of their so-called 

 wheels, and they can also crawl and hold on to any object 

 by their tail feet. The Brachions are free swimmers, and 

 can anchor by means of their tail feet, but they do not 

 crawl. These Brachions are the highest of the defensively- 

 armed sorts They are protected by shells more like 



