102 DE. ELIAS METSOHMIKOPF. 



gestion. Those around the echinus egg, on the other hand;, 

 became filled with small particles of yolk, while yet retaining 

 their complete independence one of another. I have seen the 

 same thing occur on introducing large bodies, such as glass 

 spicules, rose thorns, echinus spines, &c., beneath the skin of 

 Bipinnaria, Tethys, and Terebella, and into the deeper layers 

 of the mantle of Ascidia intestinalis. Soon after the 

 foreign substance appeared within the body, the amoeboid cells 

 (connective-tissue corpuscles in Bipinnaria and Tethys, lymph 

 corpuscles in Terebella, test-cells in Ascidia) began to collect 

 around it, finally surrounding it completely, and forming a 

 mass so large as to be easily visible to the naked eye, while 

 remaining perfectly distinct from one another, and so not 

 forming a true plasmodium. In Tethys I once saw a partial 

 fusion of cells into a complex, the component elements of 

 which were still, however, easily recognisable. It was perfectly 

 easy, by means of sections to make sure of the absence in 

 Tethys of true plasmodia in these " inflamed " regions (I 

 made use of the ear-shaped tentacles in my observations) . 



It follows from this, that while mesoderm plasmodia, when 

 they arise in the animal body, are formed round foreign sub- 

 stances, yet that this formation is not a necessary consequence 

 of the presence of such substances, it being perfectly possible 

 for the reaction of the organism against intruded matter to 

 take place without any such formation. It has also been shown 

 that one function of amoeboid mesoderm cells is to eat up those 

 parts of the organism which have become useless, and also any 

 foreign bodies which may have pierced through the ectoderm ; 

 or, if it be not possible to eat up such bodies, to surround and 

 isolate them. It is obvious that the process of removal of 

 small masses of detritus, or minute grains of carmine, on the 

 one hand, is fundamentally identical with that of surrounding 

 larger foreign bodies, on the other. Glass rods, atoms of dust 

 or carmine, are surrounded or devoured by aggregates of cells 

 in exactly the same way. It is also undeniable that the 

 results of introducing a glass spicule, or other irritant, into 

 the body of an Invertebrate, bear no small resemblance to 



