M. J. Frcnzcl on the Mesozoon Salinella. 81 



rather regard absorption in the Metazoa as a purely chemical 

 process, emanating from the living cells. 



Now, should we desire to construct a multicellular animal 

 from a number of Protozoa, e. g. from Ciliate Infusoria, we 

 should consequently soon be confronted with a great physio- 

 logical difficulty. We could indeed easily imitate the simplest 

 Metazoon ty]ie, and so arrange the cells that they should 

 surround a cavity possessing an incurrent opening. ]5ut 

 how would nutrition ])roceed ? The grou)) of Protozoa would 

 at all events obtain their food from the common cavity, but 

 it would be directly introduced into the interior of the separate 

 individuals, there digested, and so forth. It follows that in 

 this construction of ours we should not get beyond a simple 

 Protozoon colony, and should still be a long way from 

 obtaining a typical Metazoon. For although among the 

 JMctazoa there are forms which possess intracellular digestion, 

 we must nevertheless not forget that it is only the endoderm 

 cells which can be concerned therein. But yet all the other 

 tissues must be similarly nourished, and this is effected by 

 their receiving already digested matters from the intestinal 

 cells. Were we able therefore still to regard the latter at all 

 events as Protozoon cells, this view would be absolutely 

 inadmissible for the former, the cells of the mesoderm and 

 ectoderm, and they must absorb in a manner similar to that 

 of the intestinal cells which possess the power of extra- 

 cellular digestion. 



From the foregoing considerations it is not difficult to see 

 that the multilamellar character of the Metazoa in itself entails 

 the decisive diiference which separates them from the Proto- 

 zoa, and, further, that the multicellular character, as such, is 

 insufficient to bridge over the deep gulf between the two 

 principal groups of the animal kingdom. 



It is well known that the title Mesozoa has already been 

 bestowed upon oi'ganisms Avhich it must be confessed are 

 strange enough, and which rendered the justification of the 

 term not improbable. But the position of the Orthonectids 

 and Dicyemids is nevertheless an extremely doubtful one, 

 and points more to an affinity with the \vorms. The genus 

 Trichoplax^ moreover, has been with good reason assigned to 

 the Metazoa by Fr. Hchulze ; for although its conditions of 

 nutrition may be regarded as being still very obscure, never- 

 theless it has not been possible to determine that its digestive 

 processes are intracellular. 



It thus came to pass that the group Mesozoa once more 

 disappeared from the scene. I therefore consider that I am 

 entitled to regard the chance as a lucky one which enabled me 



Ann. dc Mag. N. Hist. JSer. 6. Vol. ix. 6 



