904 THE ANIMAL KINGDOM. 



Hallez has described by the name of Arcyothrix Balbianii an Amoebine found 

 by him in a vessel containing ova of Ascaris megalocephala, kept at 25C. It moves 

 upon a pedal disc, is in shape irregularly globular, has non-contractile vacuoles 

 and one contractile, with pseudopodia of two kinds, an anterior, digitiform, by 

 which food is captured, and two posterior. The latter are of great length and 

 extreme tenuity, beset with minute varicosities, and as a rule bifid. They are 

 usually directed in opposite directions, and Hallez thinks they serve like a moveable 

 net to retain the food. See Mdm. de la Socie^ des Sc. &c., Lille, (4), xiv. 1885. 

 With Arcyothrix may be compared Podostoma filigerum, a freshwater amoeboid 

 form, which possesses, in addition to ordinary pseudopodia, one or two long 

 vibratile processes used for catching food. See Claparede and Lachmann, Etudes 

 sur les Infusoires, &c., Paris, i. 1858-9, p. 441; Cattaneo, Atti Soc. Ital. Sc. Nat 

 xxi. 1879. 



Catallacta. Under this name Haeckel has described a marine organism, 

 Magosphaera planula, found by him in 1870 on the coast of Gisoe, a Norwegian 

 island some miles S. W. of Bergen. His account may be briefly summarised as 

 follows, (i) Egg-like stage, in the form of spherical cysts 'c^mm. in diameter, 

 attached to the stem of the Alga Cladophora. The cyst-membrane is tough, in- 

 distinctly laminated, and at the point of attachment either thin or perforated. The 

 contained protoplasm is yellowish; there is a vesicular nucleus surrounded by 

 a zone of granules, often disposed in radiating processes, (ii) Segmentation stage. 

 The nucleus and protoplasm undergo binary fission with successive stages, 2, 4, 8, &c., 

 until thirty-two cells are formed. The cells, at first globular, become polygonal 

 from mutual pressure, and are arranged in a single layer. Their outer surfaces 

 give origin to pseudopodial processes which are finally converted into cilia. The 

 sphere now rotates within the cyst, (iii) Volvox stage. The sphere is free-swimming, 

 07mm. in diameter. Its constituent cells are pear-shaped, their outer surfaces 

 convex and ciliated, their inner ends attenuated and united centrally ; they are 

 imbedded in a clear structureless jelly. Each cell has at its base a slowly pulsatile 

 vacuole. The vesicular nucleus surrounded by granules is median in position, 

 (iv) Peritrichous Infusorian stage. The cells are detached, and swim about by 

 means of their cilia. The body of the cell shortens, lengthens, bends from side 

 to side. The contractions of the vacuole are more rapid. The ciliated disc is 

 seen to be vertically striated, and particles of carmine brought to it by the cilia are 

 ingested, (v) Amoeba stage. The cells become amoeboid. The Amoeba is 

 characterised by its sharp-pointed pseudopodia protruded singly or in bundles. 

 From time to time a pseudopodium elongates and vibrates slowly. There is 

 a hyaline ectosarc. Carmine particles are ingested at any point of the surface. 

 Haeckel did not succeed in tracing the life-history beyond this stage. But he 

 found creeping over the Cladophora Amoebae of various sizes, with pseudopodia 

 of identical character. The nucleus of the larger Amoebae was as large as that 

 of the egg-like stage. The contractile vacuoles were increased in number, the 

 largest specimen observed having five. The Amoebae in question were crammed 

 with diatom-frustules, chlorophyl-bodies, &c. Haeckel supposes that they en- 

 cyst, and the life-history, as above-detailed, recommences. If this supposition is 

 correct, the dominant phase is an Amoeba, and Magosphaera can scarcely be 

 Classed with Flagellata as it is by Saville Kent. The organism does not appear 

 to have been seen by any subsequent observer. See Haeckel, J. Z. vi. 1871; 



