In the Vorticellm and allied forms supported by rigid or flexible pedicles the fissiparous pro cess is essentially similar. The adult bell (fig. 9, a) preparatory to its division becomes considerably extended in a lateral direction (b), in which condition the line of fissure is in dicated, extending from the mouth of the bell to the point of its connection with the pedicle. An indentation soon appears which, progres sively extending downwards, soon separates the original animalcule into two, both of' which are attached to the stem (c, d). In a short time one or both break loose ; in the former case the stem survives, in the latter it perishes. The detached bells speedily assume a new form (e,f), and might easily be mistaken for a totally different genus swimming about by means of cilia situated at both extremities of their barrel-like bodies. At last, having found a fit support, they fix themselves to it, the attached extremity becoming gradually elon g ated into a delicate irritable filament similar to that which they possessed prior to the com mencement of the fissiparous process.
Gentnziparous reproduction.— Besides the above mode of increase, many of the Vorti cellm and similarly organized forms throw out little gemmm or lateral buds in the same man ner as the Hydrce and some other Polypes, which, as they advance to rnaturity, assume the form of the parent stock, from which they at length become detached, or else remain asso ciated with the original from whence they sprung.
Sporiferous reproduction. —The gastric vesi cles of the Polygastria occupy but a small proportion of the interior of their minute bodies ; the rest is partially filled up with a granular tissue, which seems made up of nu cleated cells, or, in other words, of sporules or spawn, the germs of future progeny ready to be called into active existence when liberated from the nidus in which they were generated. In Kolpoda cucullus (fig. 18, 3), these spo rules are represented in the act of becoming discharged from the parent animalculre.
In many species of animalcules it is easy, with the assistance of a good glass, to per ceive in the interior of their bodies certain isolated sacculi endowed with very remarkable po.wers of contraction and of dilatation ; this is repeated at regular intervals ; and so great is the contractile force that the little sac seems entirely to disappear, and then in a short time slowly dilating regains its former size. These sacculi Ehrenberg at first thought to be sto machal cavities, which the creature \could alternately fill and empty ; but subsequent observations convinced him that they were or gans of a peculiar character. By slightly com pressing large specimens, such as Paramecium aurelia, he further observed that these con tractile vesicles were generally two (sometimes three) in number, occupying determinate situ ations in the creature's body, and that from each of these a number (eight) of little canals were given off' like rays from a centre towards the circumference of the body. These canals became gradually enlarged as the sacculus con tracted ; and vice versa, when the vesicle dilated the canals shrunk and disappeared. Each canal
is slightly enlarged at its origin from the central cavity', and the whole apparatus has the appear ance of two little Ophiuri, or thin-rayed star fishes, enclosed in the body of the animalcule (fzg. 18, 1 Sr 4, s, s). The contractile sacculi were seen by Ehrenberg in at least four-and twenty different species of Polygastrica ; but the radiating canals were detected in two only, viz. Paramecium and Ophryoglena.
These organs exhibit, both in their number and situation, important differences in different species. In Paramecium aurelia, Paramecium caudatam, Leucophrys sanguinea, Trachelius anas, Bursaria vernalis, and Stentor two of them are found, one situated in the middle of the anterior, and the other in the middle of the posterior, halves of the animal. All the above species, with the exception of' Stentor, multiply by spontaneous transverse division, and when thus divided each portion retains one of the contractile organs, and their being thus double seems to have same relation with the kind of fissiparous division which the animalcules undergo. At certain periods four of these sacculi are met with in several of these Infusoria, whilst at others only two are found in animalcules of the same species. When four are present, there are always two situated in each half of the body, and it is remarkable that all the Infusoria thus furnished are suscep tible both of transverse and longitudinal divi sion, so that when so divided each quarter retains one of these organs. In Euodon eueul lulus three of these vesicles are present, two of which are placed one on each side of the dental cylinder, and the third in the hinder part of the body near a dilatation of the alimentary canal in the vicinity of the anal opening. This. ani malcule likewise divides both longitudinally and transversely.
There is another organ regarded by Ehren berg as playing an important part in the organi zation of these Infusoria. This is of a roundish described, it is by no means easy to come to any satisfactory conclusion. Ehrenberg considers that the contractile organs provided with the r radiating canals cannot be regarded as hearts because their movements are so slow ; neither can he regard them as respiratory organs, which would require the presence of a vascular appa ratus more distinctly- developed than it appears to be in the Polygastric animalcules ; he is, therefore, disposed to believe them to be con nected with the generative system, and refers to them the office of fecundating the ova con tained in the interior of the body by dispersing the seminal fluid.
The opaque body above described, the same authority suggests to be the testis, believing it to secrete a seminal fluid. Both these suppo sitions are based upon a fancied analogy be tween the parts in question and certain organs which are met with in the Rotifera, and it is needless to say that they are at present purely hypothetical. (T. Rymer Jones.)