14 COMPARATIVE ANATOMY CHAP. 



The digestion of solid food takes place in the endoplasm. In it 

 lie the nucleus or nuclei. It often contains non-contractile vacuoles, 

 food vacuoles, products of excretion (crystals), fat drops, oil drops, etc., 

 gas-bubbles, pigment granules. The endoplasm occasionally shows slow 

 streamings (circulation in Infusoria). 



In the Heliozoa, the protoplasm becomes, by means of the ap- 

 pearance of numerous non-contractile vacuoles, spongy, alveolar. In 

 the Cystoflagdlata we find a central plasmic portion from which the 

 protoplasm radiates to the surface in a network forming numerous 

 vacuoles. This arrangement of the plasm resembles that in the plant 

 cells. Granular movement can be seen in the cords and strands of the 

 protoplasm ; between them lies cell-sap. 



In many true Flagdlata which take in no solid food but feed in 

 the manner of plants the protoplasm contains small pigment bodies 

 (chlorophyl or similar pigment), organs of assimilation which form 

 amylum. Chlorophyl (proper to the animal body and formed by it) 

 is also to be found in Infusoria (in a Forticella) in a dissolved form. 



Besides these there are unicellular algse, which live symbiotically 

 with many forms of Protozoa in the same way as Algce and Fungi live 

 together to form lichens (yellow cells, and pigment bodies of the 

 phseodium (?), of the Eadiolaria, chlorophyl bodies of many Infusoria). 



II. Adaptations for Loeomotion. 



The locomotion of the Amoeba (and many Monera) by means of blunt 

 processes of varying shape has been described above. In the Rhizopoda, 

 Heliozoa, and Eadiolaria, there are long filose processes of the exoplasm 

 (where such a differentiation exists) which radiate from the body on 

 all sides the so-called pseudopodia. These processes serve, however, 

 more for taking in food and as a hydrostatic apparatus than as organs 

 of active locomotion. There are two principal sorts of pseudopodia 

 myxopodia and axopodia. The former are not stiff, they are pro- 

 trusible and retractile, can fuse with neighbouring pseudopodia into a 

 network, and, chiefly in Bhizopoda, can collect into small masses by 

 flowing together outside the body at the points where they meet with 

 food. Such myxopodia are characteristic of the Rhizopoda and most 

 Radiolaria. The axopodia, which are found in the Heliozoa, and in 

 Acantharia among Eadiolaria, are, on the contrary, more or less stiff', 

 and not inclined to reticulate and fuse. In their axes there generally 

 runs a stiff axial filament, a sort of elastic organ of support formed of 

 organic substance. These axial filaments run towards the central 

 point of the body to the boundary of the endoplasm (Acfinosphavium), 

 or to the nucleus near the centre (Adinophrys), or they meet actually 

 in the centre (Acantharia). All pseudopodia show more or less swift 

 granular streamings. 



In the Rhizopoda with calcareous shells, part of the protoplasm spreads itself 

 in a layer over the latter, and from this layer the pseudopodia radiate. In the 



