THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. VI. 



Washington, D. C, April, 1885. 



No. 4. 



Abstract from an Article on Intra- 

 cellular Digestion by Dr. Elias 

 Metsclinikoit'.* 



BY n. G. BEYER, SURG. U. S. N. 



Metschnikoff has long been of the 

 opinion that many questions con- 

 nected with the genealogy of the 

 Metazoa are not to be solved by the 

 methods of purely morphological em- 

 bryology, but that in the determina- 

 tion of the phylogenetic importance 

 of any organ," a knowledge of the 

 physiological history is often indis- 

 pensable. The embryonic history of 

 an animal or organ shows us a series 

 of phenomena, often extremely com- 

 plicated, among which mere embry- 

 ology cannot, in many cases, choose 

 out those which are of primftive from 

 those of secondary importance. The 

 difficulties, he says, 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. Thus, 

 in attempting to discuss the evolution 

 of such an organ, as for instance the 

 alimentary canal, one of the oldest 

 and most widely distributed organs 

 of all the Metazoa, one must collect 

 not only embryological evidence as 

 to the mode of formation of the endo- 

 derm, but also physiological evidence 

 as to its function. 



When it became known that all the 

 lower Metazoa, such as sponges, cod- 

 lenterates and turbellarians, possessed 

 an intracellular digestion, the conclu- 

 sion, of course, was obvious, that this 

 mode of nourishment was one of the 

 few characters in the organization of 



* Read before the Biological Society of Washington, 

 March 7th, tSSj. 



the Metazoa which had been directly 

 transmitted to them from the Proto- 

 zoa, and so constituted a link, how- 

 ever small, between the two groups. 

 Now, since the colonial monads — 

 organisms which most closely re- 

 semble the lowest known Metazoa, 

 their embryos and larvae — show no 

 kind of division of labor, no separa- 

 tion into nutritive and locomotive in- 

 dividuals, the question arose as to 

 whether the lowest Metazoa had not 

 i-etained the power of using any or 

 all the cells of their body for the pur- 

 pose of ingesting food. In order to 

 answer this question, Metschnikoff 

 undertook a series of investigations 

 of the results of which we will here 

 give a brief summary. 



I. Ectodermal Intracellular Di- 

 gestion. — The sponges being at pre- 

 sent the lowest known Metazoa, it 

 seems indeed surprising that Metsch- 

 nikoff' has not been able to discover 

 any ectodermal digestion in them. 

 Repeated researches on Ascetta pri- 

 mordial is and Halisarca lobtilaris 

 gave negative results, and thus, al- 

 though not absolutely denying the 

 possibility of digestion taking place 

 within the ectodermal cells of sponges, 

 Metschnikoff" does not think it proved 

 as some would have it. More favor- 

 able objects for these researches were 

 found to be the true ccelenterates, 

 and a digestive ectoderm was indeed 

 described in a single one of these be- 

 fore Metschnikoff" undertook his re- 

 searches. Merej-Kowsky, in describ- 

 ing a Bougainvillea ., in which the 

 alimentary canal was rudimentary, 

 put forward the supposition that in 

 this medusa the food was taken in 

 entirely by the ectoderm, but, not 



