The next family, Trachelinide, contains all those non-loricated animalcules whose alimen tary canal has two distinct orifices, but of which one only, the anal, is telminal. The genera that belong, to it are very interesting- objects, and many of them of great beauty. The reader will be able readily to recognise them by the following characters :— Trachelius (neck animalcules, 5, fig. 13). These may be readily known by their exces sively elongated upper lip, which has the -appearance of a long proboscis, or rather, per haps, resembles the neck of a goose or swan, from which circumstance some species ( Tra chelius anas) have received their best known appellations. Attentive examination, however, shews that the mouth is situated at the bottom of this neck-like prolongation (3, 4, fig. 13), and not at its extremity, as was the case in Lachrymaria. The body is ciliated over its entire surface; nevertheless the movement of some species is very sluggish, locomotion seem ing rather to be effected by creeping and bending the body than by the exertion of the cilia. Some species are exceedingly voracious, as for example Trachelius vorax, figured by Ehrenberg, which is represented in the act of swallow ing a Loxodes Bursaria, of which six may be seen already lodged in the interior of its body.
Loxodes (lip animakules). These have not the neck-like appendage of the last genus, but have the upper lip dilated and hatchet-shaped.
Bursaria (purse animalcules). In these the mouth is very wide and placed laterally, with very capacious prominent lips, but without any dental structure. They are very voracious, and although generally met with in water, some species, viz. B. Entozoon, B. intestinalis, and B. cordiformis, live parasitically in the intes tines of the frog, toad, and water-newt.
The genera Spirostomurn (snail animalcules), Phialina (spigot animalcules), Glaucoma (pearl animakules), are too nearly allied to the preceding to render any special account of them necessary.
The genus Chilodon presents a very simi lar organisation, but is remarkable from the circumstance that its mouth is furnished with a tubular fasciculus of setaceous teeth, while the anterior part of its body is advanced forward in the shape of an expanded membrane or prolonged on one side, so as to form an auriculated appendage. In Nassula, likewise, a similar dental structure exists, but this will be best described hereafter.
Nutritive system.—By employing coloured organic substances as food for these animalcules, Ehrenberg at length succeeded in developing the organisation of the nutritive apparatus in these microscopic beings. For this purpose lie made use of pure indigo, carmine, sap green, and other vegetable colouring substances which are insoluble in but miscible with water, very finely levigated, and which the animal cules readily swallow, so that in a few minutes the coloured particles are distinctly visible in the interior of their transparent bodies.
From observations conducted in this manner the following results were obtained That there is no absorption of the coloured fluid through the general integument of the bodies of infusorial animalcules, although this was formerly supposed to be the only manner in wlaich they could be nourished; but, on the contrary, that they were all furnished with a special mouth and internal nutritive apparatus.
2nd. That the smallest species of Infusoria which can be observed with our instruments, even those not more than IL of a line in length, have an internal set of nutritive organs as well as the largest, so that in the Monads even four, six, or eight sacculi are visible in the interior of the body, which are obviously filled through an oral aperture.
In the genera Enchelis, Paramecium, and Kolpoda, moreover, an intestiniform tube was discovered traversing the whole length of the body, and opening by a. distinct anal orifice. To this central canal are appended numerous blind vesicles, giving the whole appamtus the appearance of a bunch of grapes. In Para mecium aurelia and Paramecium chrysalis Ehrenberg counted from one to two hundred of these vesicles, which became filled with blue, red, or green, according to the colouring matter employed.
We have, however, already, in the prece ding pages, described the different arrange ment of the alimentary canal in the va rious forms of polygastric animalcules, so that few further observations are necessary in this place. Whoever wishes to observe these little beings swallow coloured food, and thus witness the filling of the nutritive sacculi, must, in order to avoid disappointment, carefully observe that the materials he employs are per fectly pure, the indigo, carmine, and sap green sold in the shops being generally so much adulterated that the animalcules refuse to swal low it ; secondly, that it be reduced by leviga tion to the most extreme state of division— grinding it for a length of time with water on a slab, with a muller, is the best way to ac complish this. When thus prepared, by placing a little with a camel's hair brush in the drop of water which contains the animalcules, but very few minutes are required with some species to exhibit numerous vesicles filled with the co loured substance. When filled, Ehrenberg has observed that sometimes one of them will in a short time empty itself, and its contents be suddenly transferred to another, whereby it seems as if the vesicle itself had a power of voluntary locomotion, which it has not. But however easy it rnay be thus to fill the stomachal vesicles, it is by no means so easy a matter to detect the central canal to which they are ap pended, insomuch that the generality of ob servers are quite unable to detect its presence. Upon this point Ehrenberg remarks, in reply to those who have doubted its existence, that there are only some animalcules in which it is possible to see it clearly ; and it is therefore necessary to seek out such species in order to obtain a view of it. In many it is of all thing,s most difficult to see it ; but the cause of this does not lie in its absence, but in the nature of the functions it has to perform, for this canal, like the ce.sophagus of larger animals, only serves for the transmission of food, riot for its retention and digestion. It becomes dilated while food is passing through it, at will, like the mouth and cesophagus of a snake when it swallows a rabbit, and immediately collapses again, and becomes quite invisible when not actually in use.