INTRACELLULAR DIGESTION OF INVERTEBRATES. 89 



Researches on the Intracellular Digestion of 

 Invertebrates. 



By 



Dr. Ellas Uletschnikoff.^ 



I HAVE long been of opinion that many questions connected 

 with the genealogy of the Metazoa are not to be solved by the 

 methods of purely morphological embryology. Morphology 

 certainly considers as of primary importance the structure of 

 organs which have either lost their function by retrogression, 

 or which, being not yet fully developed, have not acquired 

 their full functional activity ; but in the determination of the 

 phylogenetic importance of such organs, a knowledge of their 

 physiological history is often indispensable. The embryonic 

 history of an animal or an organ shows us a series of pheno- 

 mena, often extremely complicated, among which mere em- 

 bryology cannot in many cases choose out those which are 

 primitive from those of secondary value. Every student 

 of comparative embryology knows how hard it is to determine 

 in any given case the genealogical meaning of a certain pheno- 

 menon, and how often the standard used is purely subjective. 

 These difficulties are increased by the fact that the primitive 

 Metazoa have all disappeared, so that the gap between the 

 Metazoa of to-day and the Protozoa is wide indeed. 



From what has been said, it is evident that, in attempting to 

 discuss the evolution of the alimentary canal, one of the oldest 

 and most widely distributed of all the organs of the Metazoa, 

 one must collect not only embryological evidence as to the 

 mode of formation of the endoderm, but also physiological 

 evidence as to its function. 



* Translated from the " Arbeiten a. d. Zoolog. Instit. Wieu.," 1883. 



