1885.] 



MICROSCOPICAL JOURNAL. 



63 



mous numbers of debris-granules 

 whicb are slowly absorbed during 

 the pupa stage, so that the cells 

 which contained them become filled 

 with clear vacuoles. On the meta- 

 morphosis of the pupa into a young 

 synapta, the cells begin again their 

 devouring work, collecting as before 

 beneath the ciliated ring and eating 

 up the products of disintegration. In 

 every case the disintegrating elements 

 break up into albuminoid granules 

 of various sizes which are gradually 

 eaten up and absorbed by mesodermal 

 cells. These appearances have been 

 found to so constantly accompany 

 metamorphosis that they are believed 

 to be normal and necessary events in 

 the life of an Echinoderm larva, and 

 comparable to the appearances ex- 

 hibited by the osteo-clasts in devel- 

 oping vertebrate bone. This func- 

 tion of the mesoderm is believed to 

 be present in all animals which un- 

 dergo an}' great degree of metamor- 

 phosis and especially in the compli- 

 cated larval changes occurring in As- 

 cidiaiis, in which Metschnikoft' fre- 

 quently saw wandering cells loaded 

 with debris. If this should prove to 

 be the case we should have a simple 

 explanation of such appearances as, 

 for instance, the transformation of the 

 degenerating nei"vous system into a 

 heap of blood-corpuscles, which is at 

 present believed to be due to a direct 

 morphogenetic change in the ganglion 

 cells. Many ovarian ova of Aurelia 

 aurita have been observed to become 

 surrounded by amoeboid cells and com- 

 pletely devoured. In his early inves- 

 tigation on intracellular digestion in 

 Ctenophores, Metschnikoff saw that 

 carmine-granules suspended in water 

 passed not only into the entoderm 

 cells, but also into those of the meso- 

 derm. In order to study this prop- 

 erty of mesoderm cells more exten- 

 sively, Metschnikoff' chose Bipin- 

 naria asterigeria and Phyllirho'e 

 brtcephalum^ because these animals 

 are not only transparent, but also 

 large enough to admit of the per- 

 formance upon them of simple ope- 



rations which they are hardy enough 

 to survive. If water holding indigo 

 or carmine in suspension was in- 

 jected beneath the epidermis of the 

 animal under observation, the por- 

 tions of coloring matter were after a 

 short time taken up by the ama>boid 

 cells. Two different kinds of amoe- 

 boid cells were found in Phyllirhoe — 

 one large, the other small ; the smaller 

 ones only ingested coloring matter in 

 this way ; the larger ones, although 

 bearing rosy patches, did not contain 

 solid particles. The smaller granules 

 of solid carmine were all eaten by the 

 small cells in the usual manner ; the 

 larger masses, on the other hand, were 

 surrounded by a kind of plasmodium 

 of small cells, which approached each 

 lump one by one and ffattened them- 

 selves upon it, fusing with neighbor- 

 ing cells as these arrived. In this 

 way Plasmodia arose of very different 

 sizes, some even large enough to be 

 visible to the naked eye, which might 

 be compared to the giant cells so often 

 described in vertebrates. This cer- 

 tainly confirms the observation so 

 often made by pathologists, that giant 

 cells are often found in the neighbor- 

 hood of foreign bodies, and long be- 

 fore the discovery of the tubercle- 

 bacillus one of the characteristic mi- 

 croscopical signs of tuberculosis was 

 known to be the giant cell. In all 

 those cases in which Metschnikoff' 

 found giant cells in Invertebrates thev 

 had arisen around foreign bodies, be- 

 ing always formed by the fusion of 

 separate cells, and not by a process 

 of incomplete fission, as some path- 

 ologists hold. Glass-spicules, atoms 

 of dust, or carmine are surrounded 

 and devoured by aggregates of cells 

 in exactly the same way. Metschni- 

 koff' thinks it undeniable that the re- 

 sults of the introduction of a glass- 

 spicule or other irritant into the body 

 of an Invertebrate bear no small re- 

 semblance to the phenomena of in- 

 flammatory exudation in Vertebrates ; 

 for certainly, in both cases, a number 

 of mesoderm cells collect around the 

 irritant body and act upon it as best 



