ON MICROSCOPIC DISCOVERY. 



625 



(Mr Pritchard here refers to the elaborate 

 engravings illustrating his Natural History 

 of Animalcules) , " it will be noticed that some 

 animalcules resemble spheres; others are egg- 

 aped ; others again represent fruits of various 

 inds eels, serpents, and many of the in- 

 ertebrated animals ; funnels, tops, cylinders, 

 itchers, wheels, flasks, &c. &c ; all of which 

 are found to possess their own particular 

 habits, and to pursue a course of life best 

 adapted to their peculiar constructions : thus, 

 for instance, whilst some move through the 

 water with the greatest imaginable rapidity, 

 leaping or swimming, others merely creep 

 or glide along ; and many are altogether so 

 passive, that it requires long- and patient 

 observation to discover any of their movements 

 at all. One description are perceptibly soft, 

 and yield easily to the touch; another are 

 covered with a delicate shell or horn-like coat. 

 Of the latter order there are different degrees 

 of density, as in the volvox, gonium, &c., 

 where the envelope is comparatively thick ; 

 and where, strange to say, the internal sub- 

 stance separates by the mode of propagation 

 into several portions, forming so many distinct 

 young ones, which at their birth burst the 

 envelope, and the parent becomes entirely 

 dissipated. In others of this order the shell 

 is merely a plate covering the body, resemb- 

 ling that of the tortoise : sometimes it includes 

 the body, so as to leave only two small aper- 

 tures at the extremities, and at others it is 

 bivalved, and incloses the creature, like that 

 of the oyster or muscle. 



" All vertebrated animals are either ovipar- 

 ous or viviparous, which terms sufficiently 

 designate their modes of production : but it is 

 not so with animalcules ; for, in addition to 

 these two methods, 1. Animalcules propagate 

 by a spontaneous scissure, or division of their 

 bodies into two or more portions, each one 

 forming a new creature, which, on its arrival 

 at maturity, pursues the same course. These 

 divisions take place in some genera symme- 

 trically, as in the gonia, &c. ; in others by 

 transverse, longitudinal, or diagonal sections. 

 In these latter cases the produce have forms 

 differently proportioned from those of the 

 creatures from which they spring. 2. They 

 propagate, in the manner before mentioned 

 of the volvox, and some other genera, by a 

 distribution of the internal substance of the 

 parent into a proportionate number of young 

 ones, all of which at their birth issue forth, 

 and leave behind them nothing but the enve- 

 lope, soon to be dissolved. 3. They are pro- 

 duced by germs, shooting forth from the 

 parent's sides. 4. From spawn, which in the 

 act of being shed, carries along with it a por- 

 tion of the parent animalcule." 1 



1 Natural History of Animalcules, Book 



VOL. II. 



p. 1220. 



We have not space to admit the detail of 

 a variety of additional and highly interesting 

 particulars relative to the infusoria that are 

 recorded by Ehrenberg. We may, however, 

 briefly state that the learned professor has 

 succeeded in developing the mouths and teeth 

 of these minute creatures, and has even ascer- 

 tained the number of the latter, their consis- 

 tency, and characteristic differences. He has 

 found them to be provided with assistant 

 organs of digestion, respiratory organs, and a 

 perfect vascular and nervous system. Even 

 the eyes of these tiny objects have been made 

 the subject of his examination, and many 

 remarkable particulars concerning them have 

 been ascertained. Regarding their fecundity, 

 it is sufficient to state, on the professor's author, 

 ity, that a single animalcule will in the course 

 of three or four days become a multitude of 

 separate existences, of whose number the 

 human mind can form no idea. 



" Motion,'' says Adams, " seems to be the 

 great delight of the infusoria ; they pervade 

 with equal ease and rapidity, and in all forms 

 and directions, the whole dimensions of the 

 drop, in which they find ample space lor their 

 various progressions, sometimesdarting straight 

 forward, at other times moving obliquely, then 

 again circularly : they know how to avoid with 

 dexterity any obstacles that might obstruct 

 their progress. Hundreds may be seen in a 

 drop of water in constant action, yet never 

 striking against each other. It at any time 

 the clusters prove so thick as to impede any 

 of their motions, they roll and tumble them- 

 selves overhead, creeping under the whole 

 range, force their way through the midst, 

 or wheel round the cluster with surprising 

 swiftness ; sometimes they will suddenly 

 change the direction in which they are moving, 

 and take one diametrically opposite thereto. 

 By inclining the glass in which the drop of 

 water is laid, it may be made to move in any 

 direction ; the animalcules in the drop will 

 swim as easily against the stream as with it. 

 If the water begin to evaporate, and the drop 

 to grow smaller, they flock impetuously to- 

 wards the remaining part of the fluid ; an 

 anxious desire of attaining this momentary 

 respite of life is very visible, as well as an 

 uncommon agitation of the organs by which 

 they imbibe the water. These motions grow 

 more languid as the water fails, till at last 

 they entirely cease. 



" Animalcules and insects will support a 

 great degree of cold, but both one and the 

 other perish when it is carried beyond a cer- 

 tain point. The same degree of heat that 

 destroys the existence of insects, is fatal to 

 animalcules ; as there are animalcules pro- 

 duced in water at the freezing point, so there 

 are insects which live in snow." 



