Fig. 16.

* Perhaps some of our readers may think the above strictures upon the opinions of Professor Ehrenberg, which appeared in the first edition of this work, and have been written upwards of twenty years, have now become rather antiquated. It is, however, the wish of the author to combine some account of the progressive advancement of our knowledge relative to interesting or disputed points of microscopical research with an exposition of the views generally adopted by physiologists of the present day; and as the above were the first arguments advanced against the then universally received opinions of the distinguished author of the ' Infusionsthierchen,' it has been deemed expedient to retain them in their original words. It may be proper to state that the microscope used in these and similar researches to which allusion will be made, is a compound achromatic, made by Ross, of London; and the powers employed, of 9/10, 1/2, 1/4, and 1/8 of an inch focus.

1 Since the above was written, Professor Ehrenberg has been kind enough personally to exhibit to the author his preparations of the central tube in several species of animalcules. The author's views, however, relative to the nature of the so-called stomachs remain unchanged.

(77). With respect to the central canal (fig. 16, 2,3, 4), we have not in any instance been able to detect it, or even any portion of the tube seen in the figures, much less the branches represented as leading from it to the vesicles or stomachs, as they are called. Even the circumstances attending the prehension of food would lead us to imagine a different structure; witness, for example, the changes of form which Enchelys pupa undergoes when taking prey, as shown in Ehrenberg's figure, where it is represented in the act of devouring a large animalcule, almost equal to itself in bulk, and is seen to assume a perfectly different shape as it dilates its mouth to receive the victim, with which its whole body becomes gradually distended. Such a capability of taking in and digesting a prey so disproportionate would in itself go far to prove that the minute sacculi were not stomachs, as it evidently cannot be in one of these that digestion is accomplished.

(78). Since the above was written, the views of Professor Ehrenberg relative to the organization of the nutritive organs of the so-called Poly-gastric Infusoria have been combated by many zealous observers both in this country and upon the Continent, and appear now to be universally abandoned. Mons. F. Dujardin* attributes the formation of the internal cells observable in the interior of these animalcules to the properties of a peculiar glutinous animal substance resembling living jelly, of which he supposes the lower organisms to be principally composed, and which he calls sarcocle. This substance, according to the views of M. Dujardin, spontaneously produces in the interior of its mass vacuoles, or little spherical cavities, into which the surrounding water finds access, and conveys along with it the coloured particles, but having no regularity of arrangement.

(79). According to the views of M. Dujardin, the phenomena attending the passage of aliment into the bodies of the so-called Polygastric Infusoria may be described as follows - as they occur in Amphileptus. In the interior of the body there are generally perceptible five or six vacuoles or cavities, distended with water, in which are contained monads and other substances swallowed as food. These vacuoles change their situation, advancing gradually towards the posterior extremity of the animalcule, where may be observed a vacuole or vesicle of larger size (and frequently irregular shape, its contour being lobulated), evidently formed by the union of several smaller vacuoles, which, having been successively brought into contact, have become fused together like bubbles of gas. This large posterior vesicle becoming more and more distended, its walls become thinner, and at last it opens externally by a wide lateral fissure, discharging its contents and then contracting to a comparatively small size.

If this process be that which generally takes place (as it is supposed to be by M. Dujardin), the excretory orifice will be constantly formed at that point where the internal vesicles (so-called stomachs) terminate their career after having passed through the glutinous interior of the animalcule; and in this case its position, although it is not the termination of an intestinal canal, may be sufficiently constant to afford a character of classification.

* "Recherches sur les Organismes inftrieures," Ann. des Sc. Nat. 1835.

(80). The celebrated botanist, M. Meyen*, regards the true Infusoria as being vesicular beings, having their interior filled with a kind of mucous substance. The thickness of the walls of the body, according to this observer, is in many species such as to be easily appreciated, and contains a spiral structure, which is readily perceptible, and which, as he thinks, establishes a complete analogy between these creatures and vegetable cells. In the larger kinds of Infusoria a cylindrical canal (the oesophagus) passes obliquely through the integument, and becomes dilated inferiorly, when distended with nutritive matter, to the size of the coloured globules met with in the interior of the body. The inner surface of this oesophageal tube is lined with cilia, by the action of which alimentary substances are kept in movement until they acquire a spherical shape. When the pellet thus formed becomes as large as the size of the pharynx will allow, it is expelled therefrom, and pushed into the cavity of the animalcule; a second pellet then accumulates, if any solid particles are contained in the surrounding fluid, which being in like manner impelled into the general cavity of the body, pushes the preceding one (which is now surrounded with mucosity) before it, and so successive pellets are formed one after the other, with which the cavity of the body becomes filled, giving the appearance that induced Professor Ehrenberg to consider these little beings as furnished with numerous stomachs.