1894.] Experimental Lesions of the Cerebellum. 303 



mesoglceal laminae of the basal moieties of the polyps being distinct 

 or only partially fused together, they are absolutely and indis- 

 tinguishably fused, and the mesoglcea is enormously thickened, 

 forming a coenenchymal mass resembling that of Alcyonium. The 

 mesogloea immediately surrounding the polyp cavities is devoid 

 of cells, but elsewhere it contains numerous intrusive cells, among 

 which spicules are developed. The intrusive cells are derivatives of 

 the ectoderm, and in suitable preparations numerous strands of cells 

 are seen to pass inwards from the ectoderm, between the ramifications 

 of the superficial set of endodermic canals, which is rather more 

 marked in this species than in X. garcice. It seems probable that 

 the greater part of the coenenchymal mesoglcea is formed at the 

 expense of the intrusive ectoderm cells, very few of which develop 

 spicules. 



These three species are interesting, firstly, as indicating the steps 

 by which forms with a wholly mesoglceal spicular skeleton, such as 

 Alcyonium, may have been derived from forms with an ectodermic 

 skeleton ; and, secondly, as suggesting the mode in which the ecto- 

 dermic skeleton of Heliopora may have been developed. In the 

 Xeniidae, as in the Helioporidse, the bulk of the coenenchymal 

 mesoglcea and the whole of the calcigenous elements are derived 

 from the ectoderm. In the one case the mesoglceal elements pre- 

 ponderate greatly over the calcigenous, in the other the preponde- 

 rance of the calcigenous elements has led to the formation of a dense 

 calcareous skeleton, the mesoglceal elements being reduced to a very 

 subordinate position. 



XX. "Degenerations consequent on Experimental Lesions of 

 the Cerebellum." By J. S. RISIEN RUSSELL, M.D., M.R.C.P., 

 Assistant Physician to the Metropolitan Hospital. Commu- 

 nicated by Professor V. HORSLEY, F.R.S. Received June 4, 

 1894. 



(From the Pathological Laboratory of University College, London.) 

 (Abstract.) 



The paths which degenerate after ablation of one lateral lobe of 

 the cerebellum, and after extirpation of its middle lobe, are discussed 

 in this paper. 



The former operation, viz., removal of one lateral lobe of the cere- 

 bellum, results in degeneration of all the peduncles on the side of the 

 lesion, and in the superior peduncle of the opposite side ; but no 

 fibres degenerate in the middle or inferior peduncle of the opposite 

 side. The degenerated fibres in the superior peduncle on the side 



