A spontaneous chicken sarcoma, peculiarly fissured by blood sinuses, and with a tendency to intracanalicular extension into them, has been transplanted and studied in eight successive groups of fowls. Histologically the growth is a characteristic neoplasm, while in its transfer to new hosts a real transplantation is obviously involved. The development of the first few series of transplantation tumors was very slow. They exhibited the histological structure of the original growth and had the same tendency to metastasize to the skeletal muscles. Recently the tumor has grown more rapidly and in a higher percentage of hosts. With this has come a simplification of structure to that of a pure, spindle-celled sarcoma. Fowls of an alien variety (Plymouth Rock) form quite as good hosts for the tumor as those of the sort (brown Leghorn) in which it was originally found. It has not grown in pigeons, rats, or mice. The question of the cause of the tumor is not taken up in the present paper. It has been found to be due to an agent which will pass through Berkefeld filters. The growth is quite distinct in its characters from the other two transplantable neoplasms of the fowl (a spindle-celled sarcoma, an osteochondrosarcoma) which have such a cause. No growth like it has been observed among the forty-three spontaneous tumors of the fowl that have come under our observation.