624 



SUPPLEMENT 



with the digestive functions; and hence it 

 is that Ehrenberg has selected this as the 

 leading feature of his arrangement, denomi- 

 nating his two grand divisions of the Phyto- 

 zoa, Polygastrica and Rotatoria ; the for- 

 mer of which implies such as are possessed of 

 several distinct stomachs or digestive sacs ; 

 and the latter such as have true alimentary 

 canals and rotatory organs provided with a 

 number of cilia aptly disposed for promoting 

 the objects of life : these two grand divisions 

 of the Phytozoa are afterwards subdivided 

 into families and other minor branches. The 

 cilia, in their different combinations, supply 

 the means of locomotion, propelling the crea- 

 ture, in many cases, with great rapidity 

 through the water : they are apparently stiff 

 like eye-lashes ; and from Dr Ehrenberg's 

 description of some of the larger ones, they 

 issue from bulbous substances at. their bases, 

 and being acted upon by muscular fibres, are 

 capable of being- moved to and fro in particu- 

 lar directions, so as to occasion a. current of 

 the fluid to flow towards the mouth of the 

 animalcule, by which it is furnished with 

 fresh water or food. They are sometimes 

 disposed, as before stated, round certain organs 

 of a circular form, which, on account of their 

 peculiar vibrations, giving the appearance of a 

 rotatory action, are termed rotatory organs. 

 A second curious feature in the construction 

 of some of these minute creatures are the 

 setce, or bristles, attached to the surface of their 

 bodies : these short movable hairs in all pro- 

 bability act as fins, and contribute greatly to 

 their means of motion. The third feature, 

 are the uncini, or hooks, setaceous appendages 

 curved at their extremities, and serving the 

 creature to attach itself to any object it chooses. 

 A fourth are the styli, jointed at their bases, 

 and differing from the cilia in respect of their 

 being unable to effect a rotatory motion : 

 these, however, are more flexible, and have 

 more play, than the setae. Independently of 

 these peculiarities, some animalcules possess 

 the extraordinary faculty of thrusting out, or 

 elongating, portions of their bodies at various 

 points, which, assuming the appearance either 

 of legs or fins, are termed variable processes, 

 and enable the creature to walk or swim. 



" It was a favourite hypothesis, with na- 

 turalists, some years ago, that the class of 

 animalcules under consideration was entirely 

 nourished by cutaneous absorption, and that 

 no suitable organs for transmitting and digest- 

 ing food were discoverable. Baron Gleichen 

 was the lirst who brought the truth of this 

 theory to the test ; for having tinged some 

 water containing animalcules with carmine, 

 he found on the second day that only some 

 distinct cavities, in the interior of their bodies, 

 were filled with the colouring matter, evidently 



demonstrating the existence of an alimentary 

 structure : here, however, he left the subject, 

 and it is to I)r Ehrenberg's further investiga- 

 tion of it that we are indebted for an accurate 

 description of their different forms. In more 

 recent experiments, it has been found advisa- 

 ble to employ vegetable colouring substances 

 in their pure state ; such, for instance, as sap- 

 green and indigo, which, together with the 

 valuable accession of an excellent instrument, 

 enabled the doctor to contribute much to our 

 previously imperfect knowledge of this branch 

 of natural history. 



" In the selection of vegetable substances 

 for infusions (for procuring animalcules) such 

 as stalks, leaves, flowers, seeds of plants, &c., 

 care must be taken that there be no admixture 

 of quinine (hark) in them, or the intention 

 will be frustrated. Immerse these, whatever 

 they may be, for a few days, in some clean 

 water, when, if the vessels which contain 

 them be not ;;gitated, a thin pellicle, or film, 

 will be discerned on the surface, which, under 

 the microscope, will be seen to be inhabited 

 by several descriptions of animalcules : the 

 first produced are commonly those of the 

 simplest kind, called monads. In a few days 

 more, their numbers will increase to such an 

 amazing extent, that it would be utterly im- 

 possible to compute those in a single drop of 

 the fluid. After this again, they will begin 

 to diminish in numbers, and I have gener- 

 ally observed them supplanted by others of a 

 larger species and more perfect organization ; 

 such as the cyclidia, paramesia, kufpod(e, &c. 

 It is worthy of remark here, however, that in 

 their production they do not pursue any regu- 

 lar order, even in similar infusions. If the 

 vessel be large, and the circumstances under 

 which it is placed sufficiently favourable, a 

 still higher description of animalcules will 

 succeed, viz. the vurtictlla, and lastly the 

 brachioni ; and thus a single infusion will 

 repay for the little trouble of making it with 

 a great variety of species. Water in which 

 flour has been steeped will be found to abound 

 also with animalcules : and it is remarked by 

 G. Leach, Esq., that the leaden troughs, con- 

 stantly appropriated for birds to drink out of, 

 contain several descriptions of them, and more 

 especially those of the wheel genus. In 

 ponds, too, especially in the shallow parts, 

 near the edges, and in the immediate vicinity 

 of water plants, prodigious quantities of all 

 kinds may be easily procured ; so that pos- 

 sessing as we do such myriads of them all 

 around us, that they impregnate almost every- 

 thing that we eat, drink, touch, and breathe, 

 an anxiety to know more about them, and the 

 effects they produce, cannot but be regarded 

 as rational and laudable." 



" By a careful inspection of the drawings," 



