ROTIFERA. 



307 



of their ciliated rotatory organs. They were 

 formerly classed together with the polygastric 

 animalcules (POLYGASTRIA), under the com- 

 mon name of Infusoria, on account of their 

 frequent presence with these animals in vege- 

 table infusions. Recent researches, more 

 especially those of Ehrenberg, have shown 

 that the Rotifera possess a much higher and 

 more complicated organisation than the Poly- 

 gastria ; so much so, that in any linear arrange- 

 ment of the animal kingdom, if the Polygastria 

 were regarded as the lowest beings, several 

 classes might properly intervene between them 

 and the Rotifera. We shall, however, see that 

 there are transitionary forms from the lower 

 to the higher family, sufficiently indicative of 

 their relations and the common circumstances 

 under which they are produced. 



For the discovery, and our knowledge of 

 the structure, of the Rotifera, as well as the 

 Polygastria, we are almost entirely indebted to 

 the use of the microscope. Although, gene- 

 rally, the former creatures are much larger 

 than the latter, they were not discovered till 

 after the Polygastria. We are, however, in- 

 debted for the first observation of both 

 the one and the other to the sagacity of the 

 same great observer Leeuwenhoek, who, in 

 1675, first saw the Vorticella convallaria, and, 

 in 1702, described the Rotifer vulgaris. Pre- 

 vious to this period, no accurate knowledge of 

 creatures so small existed, although the specu- 

 lations of Plato and the older Greek philoso- 

 phers, subsequently followed up by Descartes, 

 on the doctrine of living atoms, indicated that 

 the human mind had already felt the possibility 

 of the existence of such conditions of organic 

 matter. Aristotle, too {Hist. Anim. v. c. 19.), 

 as Ehrenberg has pointed out, was not un- 

 aware of the fact, that coloured water was 

 produced by worms of some kind, which 

 would seem to indicate a knowledge of the 

 existence of some of the forms of Infusoria. 



As the discovery of the first Rotifer must 

 be regarded as an era in the history of 

 zoology, we give it in the words of Leeuwen- 

 hoek himself: " On the 25th of August I saw 

 in a leaden gutter, at the fore part of my 

 house, for the length of about five feet, and 

 the breadth of seven inches, a settlement of 

 rain water which appeared of a red colour. 

 ... I took a drop of this water which I 

 placed before the microscope, and in it I dis- 

 covered a great number of animalcules. Some 

 of them red, and others of them green. The 

 largest of these viewed through the micro- 

 scope did not appear bigger than a large grain 

 of sand to the naked eye, the size of the 

 others was gradually less and less : they were 

 for the most part of a round shape ; and in 

 the green ones the middle part of their bodies 

 was of a yellowish colour. Their bodies 

 seemed composed of particles of an oval shape ; 

 they were also provided with certain short 

 and slender organs, or limbs, which were pro- 

 truded a little way out of their bodies, by 

 means of which they caused a kind of cir- 

 cular motion and current in the water : when 

 they were at rest, and fixed themselves to the 



glass, they had the shape of a pear with a 

 short stalk. Upon more carefully examining 

 this stalk, or rather this tail, I found that the 

 extremity was divided into two parts, and 

 by the help of these tails, the animalcules 

 fixed themselves to the glass ; the lesser of 

 these appeared to me to be the offspring of 

 the larger ones." This animalcule, which was 

 the Rotifer vulgaris, is so accurately described 

 by Leeuwenhoek in the same paper, as to leave 

 little to be added by future describers. Sub- 

 sequently to the time of Leeuwenhoek, who 

 in addition to the Rotifer vulgaris discovered 

 the Mclicerta ringcus, a number of species 

 were described by Joblot, Hill, Baker, Rosel, 

 Brady, and others; so that, in 1824, Bory St. 

 Vincent was enabled principally, from the 

 writings of others, to describe eighty species. 

 Up to this time no distinction had been made 

 between the wheel and other animalcules as 

 a class. This separation was effected by 

 Ehrenberg, who has not only examined the 

 structure of these creatures with great care, 

 but has added many new species to the list. 

 In his work on infusory animalcules, he de- 

 scribes 189 species in fifty-five genera and 

 eight families. 



The Rotifera, undoubtedly, deserve to be 

 called Infusoria as much as the Polygastria, 

 as they are found very generally with the 

 latter in various kinds of infusions. There 

 are some circumstances, however, under 

 which the Polygastria are developed, in which 

 no Rotifera have yet been found : thus the 

 Polygastria have been found inhabiting water, 

 containing sulphuretted hydrogen and other 

 gaseous constituents, where no Rotiferous ani- 

 malcules have been found at all. As a general 

 statement, it is true that the Rotifera are the 

 last to appear in inl'usions ; but there are many 

 instances in which Polygastria are developed 

 without the subsequent appearance of Rotifera, 

 and they disappear from infusions sooner than 

 the former. Of the 722 species of Infusoria, 

 described by Ehrenberg, he found that forty- 

 one only were commonly present in the various 

 artificial infusions, which he made in various 

 parts of the world. Of these only three 

 species belonged to the class Rotifera, viz. Co- 

 lurus uncinatus, Ictliydium podura, and Lcpa- 

 dclla ovalis. It is the appearance of these 

 animalcules in infusions, which among other 

 things have led to the question of equivocal ge- 

 neration (GENERATION); but whatever ground 

 the low organisation of some of the Poly- 

 gastria might afford for a belief in this doc- 

 trine, the Rotifera have an organisation too high 

 to allow of doubt on this point. The fact of 

 creatures so highly developed being produced 

 in infusions, would create a doubt with regard 

 to the whole theory of equivocal generation, 

 which only positive observation could set 

 aside. 



The Rotifera, although classed with the Po- 

 lygastria as " infusory animalcules," must not 

 be regarded as performing a common function 

 with them in the economy of creation, for not 

 only are there fewer species of Rotifera, but 

 they also exist in much smaller numbers. 



