ANIMALCULE. 



1)3 



and that division takes place in many ways, so that 

 the new animals might be often taken for different 

 species. Some are gemmiparous upon peduncles ; some 

 are oviparous, some ovo-viviparous, and probably some 

 are simply viviparous. It is not known whether the 

 mode is uniform in the same species ; but the pro- 

 bability is that it is not always so, but that some 

 increase both by germs and by teguments ; and that, 

 as is the case with some of the small invertebrated 

 animals which are visible to the naked eye, their 

 modes of reproduction are different at different 

 seasons. 



The natural periods of their duration are not known ; 

 neither are their seasonal appearances. It is in the 

 temperate climates chiefly that they have been 

 examined ; and in these they are mostly summer 

 animals, but appearing at greater differences of 

 period than the larger seasonal ones. A portion 

 of water in the sun and another in the shade appear 

 to be the West Indies and Melville Island to the 

 animalcules, though probably the germs of them may 

 be equally numerous in both. When the lirnna on 

 the surfaces, and the confervse and other small plants 

 at the bottoms of the shallow waters have arrived at 

 maturity and begin to decay is the time when these 

 creatures are most abundant ; but which of them 

 perish, and which hybernate after the cold weather sets 

 in, has not been ascertained. 



There is one curious fact in these occurrences ; arid 

 that is, the power which many of the species have 

 of being revived again, not from a state of torpor 

 merely, but from one of perfect dryness, in which 

 they are not to be distinguished from small and light 

 particles of microscopic mould. Analogy would lead 

 us to suppose, or rather we are certain, that the ap- 

 parent dead state of the animalcules cannot be real and 

 absolute death, because from that there can be no 

 return of the individual but by an effort of creative 

 power, and none of the matter composing the indi- 

 vidual but by the assimilating powers of another 

 living creature ; but still it should seem that all the 

 functions of life are totally suspended, and can so 

 remain for a considerable length of time. One of 

 those in which the process of being dried and again 

 reviving has been most observed is the common 

 wheel animalcule, vorticclla rotatoria, which is very 

 curious in its form and motions, and has the ad- 

 vantage of being visible to a good eye without the 

 microscope. 



While it has sufficient water, at a temperature 

 not exceeding about 110 degrees of the common 

 thermometer, it is a very active creature ; but when 

 the water is nearly exhausted by evaporation it 

 becomes languid, the motion of the wheels is sus- 

 pended, they are withdrawn and disappear ; the 

 animal shrivels, becomes hard, and if touched with 

 the point of a fine needle, it bursts in pieces, as if it 

 were a little tear of unannealed glass. One would 

 imagine that there could be no signs of death more 

 unequivocal than these ; and when the animal is 

 blown to powder by being touched with the hard 

 point, there is no question of the fact. But it is not 

 only not dead, but if sharp points are kept away 

 from it (the action of which, though most curious, is 

 inexplicable upon any known principle), it is more 

 difficult to kill than when it has the use of all its 

 members. They bear a considerably higher tem- 

 perature if perfectly dry ; but if moisture is applied 

 with the increase of temperature, the animal is in- 



stantly killed. If kept dry, and the heat not ex- 

 cessive, it can be kept for weeks, months, and even 

 years, indeed for any indefinite time ; and all that it. 

 requires to restore it again to the world of animation 

 is simply moistening it with water. 



The return of the animal to activity, as observed 

 by Leeuwenhoeck, whose observations have not been 

 surpassed for accuracy, is curious. Some revive in 

 a few minutes, others not till after several hours ; 

 and this difference in the time of resuscitation ap- 

 pears to have nothing to do with the period during 

 which the creatures have lain dormant. The animal 

 first enlarges in size, then it begins to move and 

 elongate at the head and the tail, after this the 

 wheels expand and begin to move, and the animal is 

 soon as brisk as ever. Nor is it only once that this 

 death and resurrection (so to speak) can be made to 

 take place in the same individual. Spallanzani re- 

 vived the same ones several times over, though with 

 a diminution of their numbers each time ; and at the 

 sixteenth attempt none of them revived. It should 

 seem, both from this and from the different times 

 which they take in reviving, that they are not all 

 equally strong ; but what are the differences of age 

 or other circumstances upon which the powers of 

 endurance depend, is not known. 



The fact is a most singular one in physiology ; 

 and as we cannot suppose that they have this pro- 

 perty only to be developed by experiment, we must 

 conclude that they are subject to these temporary 

 deaths and resuscitations in a state of nature ; bul 

 from their small size we can observe them only ex- 

 perimentally. Their breathing apparatus must b<> 

 different from every species of gills with which we nr<> 

 acquainted in any larger animals which breathe in 

 the water; because all these, so far as is known, 

 perish beyond the possibility of resuscitation as soon 

 as their gills become dry. That they do breathe to 

 some extent is certain, because they can neither be 

 produced nor live in vacuo ; and when cut off from 

 a supply of air they perish before the water is evapo- 

 rated, nor does it appear that, in any case, they revive 

 again after they have once ceased to perform their 

 functions in a humid state. 



Whether they are the only animals that can be 

 seasonally preserved by perfect desiccation, and again 

 revived by moisture, is a question which it would be 

 desirable to solve, as connected with the seasonal 

 history of other aquatic animals of those countries 

 where the grand alternations of the year are wet and 

 drought ;. and one would be almost tempted by ana- 

 logy to conclude that some of the leeches which 

 infest the earth of Asia (in particular) almost the 

 instant that the rains set in, and before we can rea- 

 sonably suppose that they have grown from the egg, 

 or other germ, must pass the dry season in a similar 

 state. We know that many of the plants of those 

 countries which die down into their tubers, pass the 

 season of drought with the greater safety, and grow 

 the more vigorously, the more completely that they 

 are dried while the drought lasts. So well is this 

 understood that, in many of our cultivated plants 

 (and the greater part of them are natives of warm 

 climates), we preserve their floral beauty and their 

 culinary usefulness by taking up and drying the roots 

 during the season of vegetable inaction. Other oc- 

 casions will, however, afford us a more complete 

 investigation of this curious and interesting subject ; 

 out as the animalculi are miniatures of animals, and 

 P 2 



