A comparative spate of literature during the last fifty years notwithstanding, the histology of the spleen still remains a fruitful field of controversy, rany features even of grosser structure are still in dispute. Among these may be included: the possession or otherwise of a capsule by the alpighian bodies; the occurrence of penicilli; the occurrence of ampullae; the nature of ellipsoids; the structure of the capillary vessels; the character of the reticulum. Some authors describe vessels within the .lalpighian bodies: others deny their existence. Some deny that arteries anastomose; others say they do. Not only is our general knowledge of the spleen defective but, since the literature deals only v ry sparingly with comoarative histology, facts concerning the structure of the spleen in the various domestic animals is consequently still more meagre. Kolliker (57), (58),(59), Whiting (155), and Retterer (101), (102), (103), (104), (105), (106), (107) are among the few who have contributed to our knowledge in this respect. In view of the fact that very little plastic reconstruction work has been done on the spleen it was considered that an investigation of the organ of the domestic animals by this method would throw light, not only on gross comparative histology, hut also on the general features of splenic structure. With the intention of forming a series of reconstruction models this investigation was begun. It was soon realised, however, that models of practicable dimensions could only represent a very small proportion of the entire organ and therefore, alone, were of limited value. The work consequently has been supplemented by a more comprehensive inquiry.