82 M. J. Frenzel 07i 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 liand, since it exhibits only 

 a single layer of cells, it cannot be termed a Metazoon, 

 although the digestive processes follow tlie Metazoon type. 



It follows that we are here confronted with the first and 

 only example of a connecting-link between Protozoa and 

 Metazoa. 



Salinella J 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. AYhether, 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, 

 i. e. a knowledge of the development, is so far wanting. I 

 have so far only met with larvee, which are certainly uni- 

 cellular, and moreover have an intracellular digestion, exactly 

 like a true Ciliate. The external structure of these larva? is, 

 however, of so peculiar a character, in the possession ot 

 ventral cilia, dorsal setaj, &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 icith 

 {yitracellular digestion to the adult animal icith extracellular 

 digestion is enigmatical and completely imexplained. 



Were we to attempt to construct our Salinella from an 

 aggregate 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 



