PHYLUM PROTOZOA 67 



ments of protoplasm, and feeds by ingesting various organic bodies, notably the 

 Bacilli which always occur in great numbers in decaying substances. Numerous 

 nuclei are present. 



After leading an active existence for a longer or shorter time, the protoplasm 

 aggregates into a solid lump, surrounds itself with a cyst, and undergoes multiple 

 fission, dividing into an immense number of minute spores. The cyst (Fig. 50, 

 A, tpff, 1, spg. 2) is therefore not a mere resting capsule, like that of Amoeba, 

 but a sporangium or spore-case. Its wail consists of two layers, an inner of a 

 dark purple colour and membranous texture, formed of cellulose, and an outer of 

 a pure white hue, formed of calcium carbonate. Thus the whole sporangium, 

 winch may attain a diameter of 3 or 4 mm., resembles a minute egg. From the 

 inner surface of the wall of the sporangium spring a number of branched 

 filaments of cellulose, which extend into the cavity among the spores and together 

 constitute the capillitium (B, cp.). 



The spores consist of nucleated masses of protoplasm surrounded by a thick 

 cellulose wall of a dark reddish-brown colour. After a period of rest the proto- 

 plasm emerges in the form of an amoeboid mass which soon becomes a flagellula 

 (C), provided with a single flagellum, a nucleus (tttt.), and a contractile vacuole 

 (c. vac.). The flagellulre move freely and ingest Bacilli (D, />.), and multiply by 

 fission : then, after a time, they become irregular in outline, draw in the 

 flagellum, and become amoeboid (E). The amoebube thus formed congregate in 

 considerable numbers and fuse with one another (F), the final result being the 

 production of the great amoeboid mass (G) with which we started. There is no 

 fusion of the nuclei of the amoebulae. Thus Didymium in its active condition is a 

 jAasmodium, i.e. a body formed by the concresence of amoebulae. 



2. General Remarks on the Mycetozoa. 



Speaking generally, the Mycetozoa differ from all other Protozoa in their 

 terrestrial habit. They are neither aquatic, like most members of the phylum, 

 nor parasitic, like many other forms, but live habitually a sub-aerial life on 

 decaying organic matter. They are also remarkable for their close resemblance 

 in the structure of the sporangia and spores to certain Fungi, a group of parasitic 

 or saprophytic plants in which they ai'e often included, most works on Botany 

 having a section on the Myxomycetes or " Slime-fungi," as these organisms are 

 then called. They are placed among animals on account of the structure and 

 physiology of the flagellate, amoeboid, and plasmodial phases, which exhibit 

 automatic movements and ingest solid food. The Mycetozoa are sometimes 

 included among the Rhizopoda, a course which their very peculiar reproductive 

 processes appears to render inadvisable. 



An interesting organism, called Protomyxa, probably belongs to this group. In 

 its plasmodial phase it consists of orange-coloured masses of protoplasm, about 

 1 mm. in diameter, which crawl over sea-shells by means of their long, branched 

 pseudopods, and ingest living prey. No nuclei are known. The protoplasm 

 becomes encysted and breaks up into naked spores, which escape from the cyst 

 as flagellula?, but soon become amoeboid and fuse to form the plasmodium. 



CLASS III.— MASTIG0PH0RA. 



1. Example of the Class — Euglena viridis. 



Euglena (Fig. 51) is a flagellate organism commonly found in 

 the water of ponds and puddles, to which it imparts a green colour. 

 The' body (E, H) is spindle-shaped, and has at the blunt anterior 

 end a depression, the gullet (F, ces.), from the\ inner surface of which 



F 2 



