398 



ROTIFERA. 



Whilst the Polygastria descend in structure 

 to a point where it may be well questioned, 

 whether they partake most of the animal or 

 vegetable character, the Rotifera have always 

 a decided animal character. The Polygastria 

 are even said to perform functions, such as 

 the absorption of carbonic acid and the evo- 

 lution of oxygen, which would seem to throw 

 doubt on their animality altogether ; but no 

 such function can possibly be attributed to 

 the Rotifera. They appear to be distributed 

 as widely on the earth as the Polygastria ; and 

 Ehrenberg has recorded their existence in 

 various parts of Europe, Asia, and Africa. 

 They have also been found in America. They 

 inhabit both salt water and fresh, although 

 the species which inhabit the latter are by far 

 the most numerous. Like some of the higher 

 animals, the same species are found inhabiting 

 both salt and fresh water, whilst others are 

 peculiar to brackish water. Although they 

 are capable of pursuing their way in the open 

 water, they are generally found swimming 

 around, or attached to, the leaves and other 

 parts of aquatic plants. In our own country 

 the leaves of Ceratophyllum are found to be a 

 favourite resort of species of Limnias, Masti- 

 gocerca, Dinocharis, Momira, and others. The 

 floating roots of the various species of Lemna 

 are also the favourite resort of several species, 

 whilst others are found in abundance amongst 

 the fibrilliform fronds of the fresh-water alga?. 

 Some of them even take up their residence in 

 the interior of the cells of plants. Roper 

 first discovered them in the cells of Sphagnum 

 obtusifolium. Subsequently linger described 

 a peculiar movement in certain tubercles 

 which he had observed to be developed upon 

 the stalk of Vaucheria clavata. The same phe- 

 nomenon was witnessed by Professor Morren, 

 of Liege, who, on investigating the subject 

 more closely, found that the movements of 

 the tubercles was due to the presence in their 

 interior of the Rotifer vulgaris. Others, again, 

 are found in turfy and bog waters ; whilst 

 some, especially the species of Notommata, are 

 found parasitic upon other animals. 



The Rotifera are more susceptible to the in- 

 fluence of either high or low temperatures 

 than the Polygastria. Ehrenberg observed 

 the latter constantly come to life after the 

 water in which they were contained had been 

 frozen. Species ot'Digtena, Metopidia, Column, 

 and Lepadclla frequently came to life after 

 they had been frozen for a short time. Other 

 species experimented on, as Hydatina scnfa, 

 Brachionus tirceolaris, and species of Salpina, 

 all died. Although they are easily destroyed 

 by being frozen, some of them will bear a 

 great variety of temperature. Thus the Phi- 

 lodina roseola, which we have found in the 

 streams of Yorkshire, has been discovered by 

 Professor Agassiz amongst the red snow of 

 the Alps, where it must have been exposed to 

 a much lower temperature than in the former 

 habitat. Polygastria bear also a higher de- 

 gree of heat than Rotifera. Brachionus urceo- 

 laris and Hydatina senta were found alive after 

 having been exposed for thirty seconds to a 



temperature of 104 Fah. Higher tempera- 

 tures speedily destroyed them. 



One of the most remarkable points in the 

 economy of the Rotifera is the power they 

 possess of recovering their vitality after 

 having been apparently perfectly desiccated. 

 This fact was first made known by Leeuwen- 

 hoek, who, at the same time that he disco- 

 vered the existence of the common Rotifer, 

 had an opportunity of observing this remark- 

 able property. In one of his original papers, 

 contributed to the Royal Society of London, 

 he says : 



" In October, 1702, I caused the filth or 

 dirt of the gutters, when there was no water 

 there, and the dirt was quite dry, to be ga- 

 thered together, and took about a teacupful 

 of the same and put it into a paper upon my 

 desk, since which time I have often taken a 

 little thereof, and poured upon it boiled water, 

 after it had stood till it was cold, to the end 

 that I might obviate any objection that should 

 be made, as if there were living creatures in 

 that water. These animalcula, when the 

 water runs off them or dries away, contract 

 their bodies into a globular or oval figure. 

 After the above-mentioned dry substance had 

 lain near twenty-one months in the paper, I 

 put into a glass tube, of an inch diameter, the 

 remainder of what I had by me, and poured 

 upon it boiled rain water after it was almost 

 cold, and then immediately viewed the small- 

 est parts of it, particularly that which sub- 

 sided leisurely to the bottom, and observed a 

 great many round particles, most of which 

 were reddish, and they were certainly ani- 

 malcula ; and some hours after I discovered a 

 few that had opened or unfolded their bodies, 

 swimming through the water ; and a great 

 many others that had not unfolded them- 

 selves, were sunk to the bottom, some of 

 which had holes in their bodies ; from whence 

 I concluded that the little creature called the 

 mite had been in the paper, and preyed upon 

 the aforesaid animalcula. 



" The next day I saw three particular ani- 

 malcula swimming through the water, the 

 smallest of which was 100 times smaller than 

 the above said animalcula. 



" Now, ought we not to be astonished to find 

 that these small insects can lie twenty-one 

 months dry, and yet live, and as soon as ever 

 they are put into water fall a swimming, or 

 fastening the hinder parts of their bodies to 

 the glass, and then produce the wheels, just as 

 if they had never wanted water. In the month 

 of September I put a great many of the last- 

 mentioned animals into a wide glass tube, 

 which placed themselves on the sides of the 

 glass presently, whereupon I poured the water 

 out, and then observed that several animal- 

 cula, to the number of eighteen or nineteen, 

 lay by one another in the space of a coarse 

 sand, all which, when there remained no more 

 water, closed up themselves in a globular 

 figure. 



" Some of the bodies of these animalcula 

 were so strongly dried up, that one could see 

 the wrinkles in them, and they were of a 



