596 (J, H. I)K'i;\V AND W. DM MOK(JAN. 



As one type of foreign body we cliose sterile agar jelly, 

 which has little or no irritative or toxic action on the tissues, 

 and is not removed by phagocytosis. As another type we 

 chose masses of gill-tissue and of the tissue of the digestive 

 gland, taken from an animal of the same species. Neither 

 of tliese could be injected under aseptic conditions, and both 

 were capable of removal by phagocytosis. Considerable 

 irritation was set up by the implantation of tliese tissues, 

 especially in the case of the digestive gland. This produced 

 marked degeneration of the neighbouring tissues, possibly 

 owing to the liberation of ferments and consequent digestive 

 action. 



Pecten ujaxiinns was selected for these experiments on 

 account of the laige size of its adductor muscle, which 

 presents a homogeneous mass of tissue particularly suitable 

 as a site for implantation of foreign bodies. Before making 

 this choice, experiments were tried on several other animals, 

 but it was found that in most cases the technical difficulties 

 encountered in endeavouring to make implantations into 

 small masses of tissue, and in determining the exact relation 

 of the underlying organs to the superficial anatomy, were 

 too great to lender these animals suitjible subjects for 

 experiment. 



Such experiments were tried on Carcinus maenas, 

 Pagurus bernhardus, and others of the smaller species of 

 crabs, on Palasmon serratus, Ligea oceanica. Aphro- 

 dite aculeata. Patella vulgata, Aplysia punctata, 

 Archidoris tubercubita, and many Lamellibranchs, but 

 none offered such promise of success as Pecten maxim ns. 



Methods. 



Pecten maxim us can be readily obtained in the Salcombe 

 Estuarv. It was found necessary to allow these animals to 

 become acclimatised to living in the laboratory tanks before 

 proceeding to th^ experimental work. When first placed in 

 the tanks the mortality Avas heavy, often amounting to 30 



