426 Metschunikoff on Gerim-Layers. [ May 
cells lost more or less completely the nutritive function, which 
became concentrated in the amceboid phagocytes. The very 
fine pores between the outer cells became larger, and formed 
mouth-openings similar to those so richly scattered over the 
surface of a sponge. As the colony more and more took upon 
itself the character of an individual (of the second order), the 
superficial persons (of the first order) became differentiated into 
an ectoderm or kynoblast, while the internal amceboid persons 
united to form a phagocystoblast (parenchyma or meso-endo- 
derm). When the cells of the latter, acting independently, were 
not able to master unusually large particles of, food, they formed 
a plasmodium, such as is often observed around large foreign 
bodies in the endoderm of Siphonophores or in the mesoderm 
of many animals. The metazoon, now provided with two primi- 
tive organs, steadily increased its activity, and in consequence 
the need of an abundant food-supply was likewise increased, so 
that it became necessary to prey upon vegetable and animal 
organisms of considerable size. To do this some entrance 
larger than that afforded by the pores was required, and one or 
more unusually wide openings arose, which ultimately led to the 
formation of a mouth. 
The differentiation of originally uniform individuals into loco- 
motor individuals and phagocytes finds many analogies in exist- 
ing animals, In the lower Ccelenterates, such as Hydro-polyps, 
actinias, certain Meduse (Oceania, Phialidium, Cunina), the en- 
tire endodermal lining of the gastrovascular system is able to 
feed upon bodies in the intracellular fashion. In consequence 
of this each endoderm cell is at once a phagocyte and a loco- 
motor individual, in those cases at least where the endoderm 
cells are flagellate. In other Ccelenterates, for instance, in 
glaura among the Craspedota, in Siphonophores, and Ceteno- 
phores, the endoderm is differentiated into amoeboid epithe- 
lium cells, which alone take in food-particles, and into flagellate 
epithelium cells, whose business it is to keep the current going, 
but which cannot take in foreign bodies. In the Sponges we 
_ find similar phenomena. In many representatives of this class . 
the flagellate endoderm cells act also as phagocytes, while in 
some silicious sponges this latter rôle is exclusively in the hands 
of amæboid cells, the flagellate Sg mee serving only to keep 
mp the current of waten 2 < 
* 
