2 THE MICROSCOPE AND ITS REVELATIONS. 



shall see hereafter ( 513), remains permanent in the great group of 

 Ccelenterata; though the endoderm and ectoderm are separated from each 

 other in its higher forms by the development of generative and other 

 organs between them. But in all Classes above the Coelenterates, the 

 primitive stomach has only a transitory existence, being superseded by 

 the permanent structures that have their origin in its walls. 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 worwZa-stage of higher types; and the METAZOA, in 

 which the morula takes-on the condition of an individualized organism, 

 the life of every part of which contributes to the general life of the 

 whole. 



392. 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, limited by a cell-wall, and con- 

 taining a ' nucleus. 7 For they consist of particles of protoplasm, termed 

 ('cytodes' or 'plastids') of indefinite extent, which 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 regularity and completeness that we have 

 been accustomed to regard as characteristic of higher Animals. Between 

 some of these Monerozoa (as they have been designated by Prof. Haeckel, 

 who first drew attention to them and the Myxomycetes ( 222) the Chla- 

 midomyxis ( 324) already described, no definite line of division can be 

 drawn; the only justification for the separation 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 gradation by which they ;pass into undoubted Khizo- 

 pods, leave no doubt of their claim to a place in the Animal Kingdom. 



MONEROZOA. 



\ 



393. A characteristic example of this lowest Protozoic type is pre- 

 sented by the Protomyxa aurantiaca (Fig. 279), a marine ' Moner ' of 

 an orange-red color, found by Professor Haeckel upon dead shells of 

 Spirula near the Canary Islands. In its active state is 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 belong- 

 ing to the body itself, together with foreign organisms (b c) such as 

 marine Diatoms, Eadiolarians, and Infusoria, which, having been en- 

 trapped in the pseudopodial network, are carried by the protoplasmic 

 stream into the central mass, where the nutrient matter of their bodies 

 is extracted, the hard skeletons being cast out. Neither nucleus nor 

 contractile vesicle is to be discerned; but numerous floating and incon- 

 stant vacuoles (a) are dispersed through the substance of the body. 

 After a time, the currents become slower; the ramified extensions are 

 gradually drawn inwards; and, after ejecting any indigestible parti- 

 cles it may still include, the body takes the form of an orange-red sphere, 

 round which a cyst soon forms itself, as shown at A. After a period of 

 quiescence, the protoplasmic substance retreats from the interior of the 

 cyst, and breaks up into a number of small spheres (B), which, at first 

 inactive, soon begin to move within the cyst, and change their shape to 

 that of a pear with the small end drawn out to a point. The cyst then 



