96 DR. ELTAS METSGHNIKOFP. 



the starting-point of a large series of important researches in 

 vertebrate histology and pathology ; but by the pure zoologist 

 they have remained unnoticed. 



The ingestive and nutrient functions of wandering mesoderm 

 cells are very various. ^ Their importance in the resorption of 

 parts which have become useless or harmful has already been 

 alluded to. I have been able to observe this property most 

 easily in Echinoderm larvae, especially in the Auricularia of 

 Synapta, and in the so-called Bipinnaria asterigera. In 

 both these forms large numbers of amoeboid cells appear 

 between entoderm and ectoderm, giving rise to all the skeletal 

 structures, and the cutis of the adult, and to the oral muscula- 

 ture of the larva. Their function, however, is not purely 

 morphogenetic. At the period of metamorphosis, which is, as 

 is well known, extremely complicated, and associated with the 

 loss of many larval organs, these mesoderm cells ingest the 

 cellular debris of the disappearing organs, and finally absorb 

 them. In Auricularia numbers of these amoeboid cells collect 

 beneath the ciliated rings just before metamorphosis, because in 

 this region the phenomena of resorption are mostpronounced. 

 The ciliated cells then break down into albuminoid globules, 

 which are devoured by the amoeboid elements below. Auricu- 

 laria is so transparent, and so easily obtainable, that it is not 

 difficult in this form to watch the process of ingestion and 

 absorption of debris in a single cell. The albuminoid 

 granules may remain for some time in contact with the amoeboid 

 cells, lying on their pseudopodia, and then be suddeuly swal- 

 lowed ; or the swallowing process may be so gradual as to allow 

 of the various stages being seen and drawn. The absorption, 

 like the ingestion, of these granules seems to vary greatly 

 in rapidity ; in some cases it commences at once and is soon 

 completed, while in others one can watch an ingested granule 

 for hours without noticing the slightest change. 



Resorption phenomena, similar to those just described, can 



' I may here remark that by " wandering mesoderm cells " I mean the so- 

 called amoeboid connective-tissue cells, as well as lymph- and blood-cor- 

 puscles. 



