196 



SCIENCE- G OS SIP. 



CHAPTERS FOE YOUNG NATURALISTS. 



(Continued from Ted. V., page 359.) 



ROTIFERA. 



By Walter Wesche. 



TD OTIFER A have for the niicroscopists a fascina- 

 -^-^ tion which is not difficult to understand. 

 Their high organisation, the uncertainty of their 

 position in the schemes of classification, their 

 curious life-history presenting so many unsolved 

 problems, their charming appearance, and the ease 

 with which many functions of life, such as diges- 

 tion and mastication, may he watched, all com- 

 bine to make them one of the most delightful 

 of studies. 



A group of naturalists worked at them for years, 

 and brought to that work an artistic freedom of the 

 pencil not often to be found in combination with 

 scientific training. " The Rotifera or Wheel Ani- 

 malcula," by Dr. Hudson and Mr. P. H. Gosse, is 

 the enduring monument of those labours, incorpo- 

 rating, as it does, the work of many other observers. 

 These authorities have divided the Rotifers into 

 four sub-orders : the (1) Rhizota. those which are 

 fixed or rooted in adult life, build tubes, or excrete 

 various forms of protective covering ; (2) Bdelloida, 

 which swim and creep : (3) Ploima, the free swim- 

 mers, which are further subdivided into "loricated" 

 and •' illorieated " : and a small group. (4), the 

 Scirtopoda, " that swim with their ciliary wreath. 

 skip with jointed limbs terminated in fans of setae, 

 and have no foot." 



Though the Rotifera derive their name from the 

 appearance of their ciliated heads, the mastax or 

 gizzard is of equal, perhaps of greater importance 

 in classification. This is by itself an interesting 

 study in morphology, as there is great diversity in 

 the forms. The vascular system and the contractile 

 vesicle caft in many genera be seen with clearness, 

 as can sometimes the curious vibratile tags, whose 

 use is unknown. The toes have an immense variety 

 as to length and shape, and are furnished with 

 glands which secrete a viscid fluid, that enables 

 the animalcule to attach itself to a smooth surface. 

 In many cases a brain can be seen, with a red eye 

 or pigment spot apparently placed upon it. The 

 effects of light are known to be attractive and 

 exhilarating. The male of a considerable number 

 of species has been identified, and he certainly 

 cannot be said to enjoy life, as he is without diges- 

 tive organs of any kind. In the Hydatina he is 

 comparatively large and easily studied, appears to 

 show searmentation, the vascular system, and a set 

 of muscles for drawing in the head ; the structure 

 generally can be -better seen than in Braeli ionvs, 

 the genus in which the male was first observed. 



The rotifera shown in the accompanying drawing- 

 have all been " dipped " in ponds in the north and 

 •west of London, and one or two from Epping Forest. 

 They only represent a percentage of many forms, 

 equally strange and curious in appearance, that 

 have come from the same district. Members of 

 the genus Floscalaria are the best-known tube- 

 dwellers, and are easily distinguished from others 

 of the Rhizota by the large development of the 

 cilia ; these remain motionless in the water, and 

 are spread out like a net. The curious foot forms 

 a suctorial disc, and, like the mastax, are charac- 

 teristic of the genus. F. cornuta is only distin- 

 guishable from F. ornata by a fleshy process placed 

 on one of the lobes from which the cilia spring. 

 F. i-ampamdata is much rarer. I have found it in 

 the Round Pond, Kensington Gardens, in the 

 Upper Wake, Epping Forest, and at Kensal Rise. 

 The tube has always the same gelatinous base, and 

 is quite hyaline when newly made ; but in course 

 of time grains of sand and flocculent matter ad- 

 here, and cause it to present the different appear- 

 ances shown in the drawing. I was only once 

 fortunate enough to take Stephanoeeros eichorno . 

 and then I had to journey to Epping to the Upper 

 Wake to secure that species. It certainly is the 

 most beautiful and imposing of all rotifers ; it is 

 so well known that description is superfluous, but 

 it may be pointed out that, as in Floscalaria there 

 are five lobes, so in Stephanoeeros are five ciliated 

 arms. Two arms in Stephanoeeros eieJwrnii do not 

 appear in the accompanying drawing, as they are 

 hidden by those on the left and right, and the 

 cilia are depicted as usually seen : but viewed with 

 " dark ground " illumination, they are found to be 

 very much longer and thicker, and form quite a 

 filamentous net in the water. I am indebted to 

 Mr. C. F. Ronsselet for a demonstration of this, by 

 means of one of his admirably mounted prepara- 

 tions of Rotatoria. 



Oer-isfes serpentinus has only an apology for a 

 tube, usually a little flocculent matter. The most 

 curious thing about the animalcule is a pair of 

 minute hooks which show when the cilia are 

 retracted. It is not common : I have taken it in 

 the Leg of Mutton Pond, Hampstead, and the- 

 Round Pond, Kensington. O. stygis makes a rather 

 untidy squat tube ; this, however, when placed in 

 the centre of a grove of bright green vegetation 

 made a very charming microscopic picture. The 

 ciliated wreath is sinele. and there are two 



