the sarcode, by which the morphological value of the rhizopod body as cell or cell-aggregate is placed beyond all doubt. There are also forms in the protoplasm of which no trace of a cell-nucleus has been found. In such, either the protoplasm of the nucleus is not differentiated as a separate structure (the monera of E. Haeckel), or we have to do with a transient non-nucleated stage in the life-history." If the sponges be included in this class it is true that in them there is a "syncytium or layer of structureless sarcode;" but of it Dr. Nicholson says—"Others of the sarcodes again become indistinguishably amalgamated with one another in progress of growth, and thus give rise to a so-called 'syncytium' or layer of structureless sarcode."
Whenever a structureless, or apparently structureless, sarcode occurs among rhizopods, we may well believe that it has arisen in them, as in their allies the sponges, through the instrumentality of cells. In higher animals I think Mr. Spencer is demonstrably wrong in supposing that any tissues arise independently of cells. Fibrous tissue certainly results from cell-formation and modification. Bone and cartilage are, it is true, not entirely cellular, but in both the interstitial substance between the cells, a product of their activities, is au exaggerated and modified cell-envelope. Therefore, since in animals higher than the rhizopods cells are universal, and since in animals lower than the rhizopods (the lower unicellular organisms) they are of course also universal, it would be inexplicable if in the intermediate animals, the rhizopods, which presumably mark a stage of evolution between the higher and the lower, cells were not present.
The animal body, in Mr. Spencer's opinion, is a sort of crystal. It is to be regarded as compounded essentially of "physiological units" of very highly complex
