POLYGASTRIA. 



furnished with two preparatory to its separation 

 into two individuals. In some species, how- 

 ever, two are constantly present. These pro- 

 boscides may possibly discharge a double func- 

 tion, and perform the duty both of locomotive 

 and of prehensile organs with which to collect 

 nourishment. 



In the Cryptomonadinidae likewise one or 

 two filiform proboscides, similar to the above, 

 seem to be the locomotive organs; and the 

 vibratile apparatus that serves for the move- 

 ments of the Volvoces is entirely composed of 

 similar structures belonging to the individual 

 animalcules that constitute the compound bo- 

 dies of these wonderful beings. 



Amongst the Vibrionidae the locomotion is 

 of a very different character. In the true 

 Vibrios it is performed by a kind of meandering 

 or undulating movement, the fibre-like com- 

 pound body of the animal bending and straight- 

 ening itself alternately, the cause of which seems 

 to depend upon a stronger binding together 

 and subsequent relaxation of the individual 

 animalcules, so that these seem to displace one 

 another. In Bacterium the contraction is 

 weaker, so that no undulating movement is 

 produced, although the creature swims straight 

 forward. 



In the family Closterina (6, 7, fig. 5) the lo- 

 comotive organs consist of numerous short, soft, 

 conical papillae, situated near the openings of 

 the shell at the two opposite extremities of the 

 animal ; they are placed upon the inner side, 

 and can be protruded but a very little way from 

 the shell. 



In the family Amoeba no special locomo- 

 tive organs are met with. The round, gelati- 

 nous, and highly contractile bodies of these 

 creatures have the capability of thrusting out 

 at will foot-like processes from any part of their 

 body, by the assistance of which they manage 

 to move about. A similar mode of progression 

 is met with in the Arcellinidae. In all the 

 higher forms of Polygastric Infusoria locomo- 

 tion is effected by means of cilia variously 

 distributed over different parts of the body, 

 but their position in different genera will be 

 described when speaking of the external forms 

 of the different families. 



These cilia are described by Ehrenberg to 

 be minute hairs arising from a thick bulbous 

 basis, upon which they execute a rotatory mo- 

 tion, some of them being continuous with their 

 basis, while others are only articulated there- 

 unto ; of these the former kind exists in Stylo- 

 nychia mytilus, and the latter in Paramecium 

 aurelia. 



In addition to the cilia some forms of ani- 

 malcules (Ox i/trichina) possess seta, which 

 are likewise stiff moveable hairs, but which 

 are without any power of vibration ; these 

 organs are used in standing and climbing. 

 Sometimes they are without any thickened basis, 

 as in Actinophrys ; generally they are pointed, 

 but occasionally have a knob at the end. 



A fourth set of locomotive organs are the styli. 

 These are thick straightsetae, which in some forms 

 of animalcules are attached like the tail fea- 

 thers of a bird to the hinder part of the body ol 



the animalcule : such styli do not vibrate like 

 cilia, neither are they implanted in a bulb-like 

 basis, nor bend like hooks, but serve merely 

 as instruments of support, or are useful in 

 climbing the stems of aquatic plants. 



Lastly, many races are furnished with uncini 

 or booklets ; these are merely bent, hook-like 

 sette, which, being thick and strong, and situ- 

 ated upon the ventral surface of the animal- 

 cule, seem to take the place of feet : they do 

 not vibrate, but are implanted into a bulb-like 

 root, which permits them to be moved in all 

 directions ; and although they are not articu- 

 lated, they resemble very much the limbs of 

 articulated animals. 



So various, however, are the forms of the 

 different families of Polygastric animalcules, 

 that the above general view of their locomotive 

 organs gives but a very imperfect idea of this part 

 of their economy; and it will, therefore, be ne- 

 cessary, before we proceed further, to describe 

 more at length some of the most interesting ge- 

 nera belonging to the class, for so strange and re- 

 markable is the organisation of some of them 

 that no generalisation would answer our present 

 purpose. Some are single and isolated indivi- 

 duals, moving freely wherever they list ; others 

 are strangely compounded of aggregations of 

 numerous animalcules associated into one com- 

 mon body, all of which must cooperate in 

 rowing about the microcosm which they col- 

 lectively form ; some are affixed to highly irri- 

 table stems, whereby they are attached to various 

 foreign bodies; some are naked, others covered 

 with shells : in short, nothing but a rapid 

 glance at the whole group will enable us satis- 

 factorily to discuss the many curious circum- 

 stances discovered in connection with their 

 history. 



The family MONADINIDJE embraces nume- 

 rous animalcules, which, however different in 

 external appearance, are evidently related to 

 each other in all essential parts of their struc- 

 ture. 



The Monads, properly so called, are so small 

 that the utmost penetration of the miscroscope 

 is insufficient to display their outward form 

 with any degree of distinctness, much less to 

 reveal their internal structure, some of them 

 being not larger than from the 1,000th to the 

 3,000th of a line, or the 36,000th part of an 

 inch in diameter. Under the highest powers 

 of the microscope they have the appearance of 

 almost invisible globular active specks, swim- 

 ming about with the greatest facility, and never 

 impinging against each other during the rapid 

 dance that they continually execute. Their 

 numbers are absolutely beyond human appre- 

 ciation, as may be readily understood from the 

 following computation of the multitudes some- 

 times met with. 



The Mimas crepusculum, found in infusions 

 of putrid flesh, crowds the drop of water in 

 which it is found to such an extent that there 

 seems to be no interspace whatever between 

 the individual animalcules. Supposing these 

 animalcules to be, as is generally the case, 

 ^th of a line in diameter, their number will 

 then amount, in a drop of water of the size of 



