MICROSCOPIC FOKMS OF ANIMAL LIFE. 11 



sion also takes place, in which the escaping segment and the one left be- 

 hind in the old shell remain attached by their pseudopodia, and the 

 former develops a new shell without undergoing any change of condition. 

 399. Heliozoa. The Actinophrys sol, sometimes termed the ' sun-ani- 

 malcule' (Fig. 285), is one of the commonest examples of this group; 

 being often met-with in lakes, ponds, and streams, amongst Confervas 

 and other aquatic plants, as a whitish-gray spherical particle distinguish- 

 able by the naked eye, from which (when it is brought under a suffi- 

 cient magnifying power) a number of very pellucid, slender, pointed 

 rods are seen to radiate. The central portion of the body is composed 

 of homogeneous sarcode, inclosing a distinct nucleus with a large nucle- 

 olus (as in Fig. 287, N) ; but the peripheral part has a f vesicular ' aspect, 

 as in the type next to be described (Fig. 286). This appearance is due 

 to the number of ' vacuoles ' filled with a watery fluid, which are included 

 in the sarcodic substance, and which may be artificially made either to 

 coalesce into larger ones, or to subdivide into smaller. A ' contractile 

 vesicle/ pulsating rhythmically with considerable regularity, is always to 

 be distinguished, either in the midst of the sarcode-body, or (more com- 

 monly) at or near its surface; and it sometimes projects considerably 

 from this, in the form of a flattened sacculus with a delicate membra- 

 nous wall, as shown at o. The cavity of this sacculus is not closed ex- 

 ternally, but communicates with the surrounding medium; not, however, 

 by any distinct and permanent orifice, the membraniform wall giving 

 way when the vesicle contracts, and then closing-over again. This al- 

 ternating action seems to serve a respiratory purpose, the water thus 

 taken-in and expelled being distributed through 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 re-fills. 

 The body of this animal is nearly motionless, but it is supplied with 

 nourishment by the instrumentality of its pseudopodia; its food being 

 derived not merely from Vegetable particles, but from various small 

 Animals, some of them (as the young of Entomostraca) possessing great 

 activity as well as a comparatively high organization. When one of 

 these happens to come into contact with one of the pseudopodia (which 

 have firm axis-filaments clothed with a granular sarcode), this usually 

 retains it by adhesion, but the mode in which the particle thus taken 

 captive is introduced into the body, differs according to circumstances. 

 If the prey is large and vigorous enough to struggle to escape from its 

 entanglement, it may usually be observed that the neighboring pseudo- 

 podia bend over and apply themselves to it, so as to assist in holding it cap- 

 tive, and that it is slowly drawn by their joint retraction toward the 

 body of its captor. Any small particle not capable of offering active re- 

 sistance, on the other hand, may be seen after a little time to glide towards 

 the central body along the edge of the pseu'dopodium, without any visi- 

 ble movement of the latter, much in the same manner as in Gromia. 

 When in either of these modes the food has been brought to the surface 

 of the body, this sends over it on either side a prolongation of its own sar- 

 code-substance; and thus a marked prominence is formed (Fig. 285 c), 

 which gradually subsides as the food is drawn more completely into the 

 interior. The struggles of the larger Animals, and the ciliary action of 

 Infusoria and Rotifera, may sometimes be observed to continue even after 

 they have been thus received into the body; but these movements at 

 last cease, and the process of digestion begins. The alimentary sub- 



