Page:Natural History Review (1861).djvu/474

462 II.—In Actinophrys and its allies there is a degree of definiteness in the form and arrangement of the pseudopodia, which contrasts strongly with the entire indefiniteness which prevails throughout the Reticulose order. These organs are, for the most part, simple filaments, tapering gradually from base to point, usually maintaining their isolation throughout, and extending in a radiary direction from the body of the animal. It is obvious that they are of much firmer consistence than in and its allies, since they neither subdivide themselves by ramification into finer filaments, nor do they show any readiness to coalesce when they come into mutual contact. Still it is equally certain that they can be retracted into the general mass of the body, and fused (as it were) into its substance; and such a fusion takes place when food is being entrapped by their means. A careful examination of the substance of the Actinophrys serves to explain this apparent inconsistency; for it thence appears that the body and its pseudopodian extensions are far from having the homogeneousness of those of Lieberkühnia, but that there is an incipient differentiation of their substance into two dissimilar constituents, the outer layer being least granular and of firmer consistence, whilst the contained portion approaches more nearly to the character of a liquid, as may be seen by the freer movements of the granular particles which are suspended in it. These two constituents have been appropriately designated by Dr. T. Strethill Wright as the "ectosarc" and the "endosarc." There is no definite line of demarcation between them; but the one graduates insensibly into the others. It seems to be, however, from the ectosarc alone that the pseudopodia are put forth; the granular endosarc not extending itself into them. A movement of granules along their surface may indeed be discerned by careful observation; but these appear to be merely particles which have been entrapped by adhesion to the surface of the pseudopodia, and are being transmitted to the body; and there is nothing like that regular circulation from the body to the extremities of the pseudopodia, and back again, which is so remarkable a feature in the Reticularia. With the incipient differentiation of the protoplasmic substance, there seems to be associated the presence of a "nucleus;" which, however, is not so strongly marked in Actinophrys as it is in Amœba, and may easily escape notice. The "contractile vesicle," on the other hand, is always discernible, and its actions are very regular. Its presence may be considered as superseding the necessity of the general protoplasmic circulation; since it can scarcely be doubted that its function is to maintain a continual movement of nutritive fluid among a system of channels and vacuoles excavated in the substance of the body, some of the vacuoles which are nearest the surface being observed to undergo distention when the vesicle contracts, and to empty themselves gradually as it refills.

The general characters of Actinophrys, with a more or less complete limitation of the pseudopodia to one portion of the body, necessitated by its enclosure within a membranous or chitinous