16 



POLYGASTRTA. 



acrite animalcules it is almost needless to say that 

 no muscular fibres are obvious, although their 

 bodies are capable of various contortions, and 

 some of their movements under the microscope 

 are extremely brisk and active. Nevertheless, 

 in some of the Vorticellinae, (Vorticella, Stentor, 

 Carchesium, Opercularia,) Ehrenberg consi- 

 ders that their presence has been detected, and 

 has even assigned their direction, some being, 

 as he asserts, longitudinal and others trans- 

 verse. In the stems or pedicles of Carchesium 

 and Tintinnus this appearance of muscular 

 fibre is more especially evident; and when we 

 consider the highly organised condition of the 

 genera in question, there seems to be no physi- 

 ological reason for considering their existence 

 improbable. 



Nervous system and organs of sense. No 

 nervous fibrils have as yet been discovered in 

 any polygastric animalcule, and, in accordance 

 with this acrite condition, no special instru- 

 ments of sensation could, according to all phy- 

 siological analogy, be expected to exist; never- 

 theless, in many genera the existence of one or 

 two minute spots of a brilliant red colour is 

 conspicuous, which are invariably found to 

 occupy the same position in a given species 

 possessed of them. These red spots are gene- 

 rally pronounced to be eyes, although for what 

 reason, except that they correspond in colour 

 with the acknowledged eyes of some of the 

 lowest forms of the Articulate, it is difficult to 

 conjecture. In two species indeed, (Euglena 

 longicauda and Amblyophys,) Ehrenberg says 

 he saw a " clear sharply defined ganglion," 

 (einen hellen, scharf umgrenzten Markknoten,) 

 under the red eye-spot, without, however, 

 offering the slightest proof that the clear 

 sharply defined body " in question was com- 

 posed of nervous matter. Should, however, 

 Ehrenberg's surmises, (for these assertions are 

 nothing more,) be correct, we should indeed 

 encounter in the Infusoria an apparatus of 

 vision of the simplest possible description, con- 

 sisting merely of a brain and a coat of coloured 

 pigment, thus dispensing both with the refract- 

 ing media that usually constitute an eye, and 

 the nervous communication generally found 

 between it and the brain. Be this as it may, 

 the Polygastria are evidently possessed of 

 considerable perceptive power, (those without 

 red spots quite as much so as those provided 

 with them ;) however rapid their movements, 

 they can steer their course with accuracy, and 

 avoid impinging against each other ; they can 

 likewise perceive the slightest contact, and 

 some species, such as the Vorticellinae for ex- 

 ample, exhibit a most exquisite sensibility of 

 touch. 



Secretions. Several species of Polygastria 

 secrete a peculiar fluid of a beautiful violet 

 colour, which is poured into the intestinal 

 canal, where it colours the excrements with 

 which it is expelled from the body. In Nas- 

 sula ornata, (I 9 fg. 16,) the apparatus for 

 secreting this fluid is situated at the anterior 

 part of the body, where it is recognisable as an 

 irregular square spot of a violet colour, situated 

 upon the dorsal surface of the body immedi- 



ately opposite to the dental cylinder. This 

 spot is composed of a great number of little 

 violet globules of unequal size, or, to speak 

 more correctly, of an aggregation of colourless 

 vesicles filled with a violet-coloured fluid. 

 From this spot a canal may be traced running 

 along the back, resembling a string of pearls, 

 in which the violet secretion is conveyed to- 

 wards the posterior part of the body. It is 

 only in the posterior third of the body that 

 there seems to exist a direct union between this 

 canal and the alimentary apparatus, for at this 

 point the violet colour of the secretion becomes 

 altered and mixed with foreign matter. In all 

 these Infusoria the violet secretion is expelled 

 through the anal orifice situated at the hinder 

 part of the body, either by itself or in con- 

 junction with the excrements. The aggrega- 

 tion of vesicles situated in the back of the 

 neck seems to be the secreting organ of this 

 remarkable fluid, seeing that no vessels could 

 be detected in communication with it, and 

 the surrounding parts were quite transparent 

 and colourless. Ehrenberg believes that the 

 violet liquid, which is of a slightly viscid 

 or almost oily character, possesses some dis- 

 solving power, for he has noticed in the 

 alimentary canal of animalcules which con- 

 tained a large proportion of it, that frag- 

 ments of oscillatorise and other substances taken 

 as food were always discoloured, divided, or 

 decomposed apparently by its action. 



Reproduction. Not the least remarkable 

 feature in the history of the Polygastria is their 

 extraordinary fecundity, which indeed far ex- 

 ceeds that of any other class of animals. The 

 infusorial animalcules, constituting as they do 

 the basis of the great pyramid of the animal 

 creation, the living pasturage diffused through 

 the waters of our globe, on which innumerable 

 creatures have to feed, must be multiplied in 

 proportion to the vast demand for food of this 

 description; and, accordingly, their multiplica- 

 tion is effected in various ways, all of which 

 are so prolific that it becomes no longer a 

 matter of astonishment that they swarm to such 

 an extent in every drop of stagnant water, or 

 that their exuvise are found in many localities 

 accumulated in such abundance, that strata of 

 soil and even vast rocks seem to be entirely 

 composed of their remains. 



Fissiparous generation. This mode of re- 

 production consists in the spontaneous fissure 

 of the original animalcule into two or more di- 

 visions, each of which soon becomes complete 

 in all its parts, and again divides in a similar 

 manner. The different steps of this process, 

 which may easily be witnessed, are in ordinary 

 cases as follows. The body of the parent is 

 seen, on its arrival at maturity, to become in- 

 tersected by a transparent line, which divides it 

 into two equal halves. In a short time this 

 transparent line becomes indented at each ex- 

 tremity, and, as the indentations become more 

 pronounced, the original creature becomes evi- 

 dently converted into two, which are united 

 together by a kind of isthmus, (figs.\7 & 18 ) 

 and at length, the isthmus becoming continu- 

 ally more and more attenuated, the slightest 



