IT PHYLUM PROTOZOA 69 



of Amoeba, but a sporangium or spore-case. Its wall 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, which 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 

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

 flagellula (C), provided with a single flagellum, a nucleus (nu.), and a contractile 

 vacuole (c. vac.). The flagellulse 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 amoebulae 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 amcebulae. Thus Didymium 

 in its active condition is a plasmodium, i.e. a body formed by the concrescence 

 of amoebulae. 



2. GENERAL REMARKS ON THE MYCETOZOA. 



Generally considered, the Mycetozoa differ from all other Protozoa in their 

 terrestrial^abit. 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 resem- 

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

 of parasitic or saprophytic plants in which they are 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 flagellulse, but soon become amoeboid and fuse to form the 

 plasmodium. 



CLASS III. MASTIGOPHORA 



1. EXAMPLE OF THE CLASS Euglena viridis. 



Euglena (Fig. 52) is a flagellate organism commonly found in 

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

 The body (^t) is about 0*1 mm. in length, is spindle-shaped, and has 

 at the blunt anterior end a depression, the gullet (A, B, gul.), from 

 the inner surface of which springs by two roots a single long flagellum 

 (fl.). The organism is propelled through the water by the lashing 

 movements of the flagellum, which is always directed forwards ; 

 it can also perform slow worm-like movements of contraction and 

 expansion (C-F), but anything like the free pseudopodial move- 

 ments which characterise the Rhizopoda is precluded by the presence 

 of a very thin membrane or cuticle which invests the body. Oblique 



