278 J. H. ASHWORTH. 



and usually fusiform, triradiate, or stellate in shape, the angles 

 of the cell being produced into nerve fibrils. 



On tracing the fibrils outwards from the mesogloea into the 

 ectoderm, they are seen to be in connection with small cells 

 which are situated in the deeper part of the ectoderm. Owing 

 to the irregularity of the inner face of the ectoderm, and to 

 the presence of spicules in the portion of the layer where the 

 nerve-cells are situated, it is not possible to obtain a section 

 which shows the ectodermic nerve plexus clearly, but small 

 portions of it may be seen where the spicules are slightly less 

 numerous. 



In the case of the endodermic nerve plexus this difficulty 

 does not exist, and an oblique section through the wall of a 

 polyp shows that the plexus of fibrils in the mesoglcea is con- 

 nected with minute stellate cells situated upon the outer face 

 of the muscle processes of the endoderm cells. Hsematoxylin 

 (especially Heidenhain's iron hsematoxylin and Meyer's acid 

 heemalum) stains the nerve-cells and fibres most clearly. 



History of our Knowledge of the Buds of the 

 Xeniidae. 



Besides the fully developed polyps, the description and 

 measurements of which are given above, there are on most of 

 the branches of the colony young polyps or buds in various 

 stages of development. These buds are invariably found at 

 the edge of the umbrella-shaped area at the end of the stem. 

 On one stem (fig. 1, left) there are ten small buds varying in 

 length from '5 mm. to 3 mm., and about fifty larger polyps 

 from 5 mm. to 10 mm. in length. The smallest buds have 

 simple tentacles devoid of pinnules, and all stages between 

 these and the adult polyps may be found. As the polyps (both 

 young and old) of Xenia are non-retractile, this genus offers 

 considerable advantages for the study of the development of 

 the polyps, and the young polyps have been noticed by many 

 observers. 



Quoy and Gaimard (1833) first observed these small polyps in 



