82 M. J. Frenzel on the Mesozoon Salinella. 
to discover, in a solution of salt obtained from a salt-pit in 
the province of Cordova, in the Argentine Republic, a micro- 
scopic animal, which, being a combination of a number of 
cells to form a single organism, cannot be regarded as a 
Protozoon ; while, on the other hand, since it exhibits only 
a single layer of cells, it cannot be termed a Metazoon, 
although the digestive processes follow the Metazoon type. 
It follows that we are here confronted with the first and 
only example of a connecting-link between Protozoa and 
Metazoa. 
Salinella, as I have named this new animal, is a multicellular 
organism in which the elementary organisms of which it is 
composed have so completely renounced their independence, 
that there has been developed an animal possessing a mid- 
gut as it were, an animal the intestinal epithelium of which is 
composed of typical mid-gut cells. Whether, nevertheless, 
there was in this case originally a colony of Infusoria, which 
have gradually become transformed, is a question which it is 
absolutely impossible to decide in any way whatever ; for 
unfortunately one of the most material aids to demonstration, 
7. e. a knowledge of the development, is so far wanting. I 
have so far only met with larve, which are certainly unz- 
cellular, and moreover have an ¢ntracellular digestion, exactly 
like a true Ciliate. The external structure of these larve is, 
however, of so peculiar a character, in the possession of 
ventral cilia, dorsal sete, &c., that we are bound at once to 
recognize their connexion with Salinella, and are inclined to 
conclude that development is thoroughly direct. This never- 
theless leaves a difficulty of considerable importance to be 
surmounted, in that the transition from the single cell with 
intracellular digestion to the adult animal with extracellular 
digestion is enigmatical and completely unexplained. 
Were we to attempt to construct our Salinella from an 
ageregate of Ciliate Infusoria, we should obtain, as we already 
know, merely a Protozoon colony. It would then be further 
necessary to induce the individual elementary organisms to 
close their mouths, empty their digestive ferments into the 
common cavity of the intestine, and absorb the digested 
matter. This would, however, constitute a highly compli- 
cated developmental process, to which there scarcely exists 
anything analogous. 
As a matter of fact moreover Nature appears to have 
followed a different path ; for an observation, which unfor- 
tunately could not be further continued in consequence of an 
unlucky accident, points to the fact that within the larval 
cell, by means of a kind of endogenous cell-formation upon 
