PROTOZOA PROTOMYXA 727 



them. But 4n all classes above the coelenterates the primitive 

 stomach forms a part, and often only an insignificant part, of the 

 whole digestive tract. Thus the whole animal kingdom may be 

 divided, in the first place, into the PROTOZOA, which are either single 

 cells or aggregates of similar cells corresponding to the morula- 

 stage of higher types ; and the METAZOA, in which the morula takes 

 on the condition of an individualised organism, the life of every part 

 of which contributes to the general life of the whole. Putting this 

 important truth into other word*, we may say of the Protozoa that 

 they are either unicellular or unicellular aggregates, while the 

 Metazoa are multicellular, and their constituent cells have different 

 functions. 



The lowest of the Protozoa, however, like the simplest proto- 

 phytes, do not even attain the rank of a true cell, understanding 

 by that designation a definite protoplasmic unit (plastid), which is 

 limited by a cell- wall, and contains a ' nucleus.' For they consist 

 of particles of protoplasm, termed ' cytodes,' of indefinite extent, 

 w r hich have neither cell-wall nor nucleus, but which yet take in and 

 digest food, convert it into the material of their own bodies, cast out 

 the indigestible portions, and reproduce their kind, with the regu- 

 larity and completeness that we have been accustomed to regard 

 as characteristic of higher animals. With regard, however, to this 

 apparent absence of a nucleus we have to bear in mind that the 

 progress of research is continually diminishing the number of forms 

 devoid of a nucleus, or, at any rate, of a nuclear material scattered 

 throughout the substance of the plastid ; in retaining, therefore, the 

 group of non-nucleated Protozoa we are acting on the principle of 

 not going beyond our evidence, and by no means reflecting on the 

 later systematists who have merged the various types (whether 

 nucleated or non-nucleated) among other divisions of the Protozoa. 

 Between some of these Monerozoa (as they have been designated 

 by Professor Haeckel, who first drew attention to them) and the 

 Myxomycetes or the Ghlamyclomyxa already described, no definite 

 line of division can be drawn, the only justification for the separa- 

 tion here adopted being that the affinities of the former seem to 

 be rather with the lowest forms of vegetation, whilst the whole 

 life-history of the types now to be described, and the connected 

 graduation by which they pass into undoubted rhizopods, leave no 

 doubt of their claim to a place in the animal kingdom. 



MONEROZOA. 



A characteristic example of this lowest protozoic type is presented 

 by the Protomyxa aurantiaca (fig. 567), a marine ' moner ' of an 

 orange-red colour, found by Professor Haeckel upon the dead shells of 

 Spirula which are so abundant on the shores of the Canary Islands. 

 In its active state it has the stellar form shown at F, its arborescent 

 extensions dividing and inosculating so as to form a constantly 

 changing network of protoplasmic threads, along which stream in all 

 directions orange-red granules, obviously belonging to the body 



