PROF. G. J. ALLMAN ON LIMNOCODIUH VICTORIA. 135 



The four perradial tentacles contract independently of the others, 

 and seem to form a different system. 



The outer surface of the umbrella (exumbrella) is covered with 

 an epithelium composed of flattened hexagonal cells, with very 

 distinct and brilliant nucleus. The subumbrella is also covered 

 with an epithelium formed of broad clear hexagonal cells, in which 

 the nuclei are distinct, but the cell-boundaries far less obvious 

 than in the outer epithelium. 



Between these two layers is included the gelatinous substance 

 of the umbrella. This is a clear homogeneous mass with stellate 

 cells scattered through it. The stellate cells cousist of small 

 spherical masses of granular protoplasm, destitute of a membrane, 

 usually containing a vacuole, and emitting from two to six long, 

 radiating, very slender, simple or branched processes, which are 

 extensions of their granular substance. 



The manubrium is composed of an outer, clear colourless ecto- 

 derm and an inner, coloured endoderm. The ectoderm is a con- 

 tinuation of the epithelial covering of the subumbrella, here much 

 thickened, and consisting, like it, of hexagonal nucleated cells. The 

 endoderm, in that part of the manubrium which lies between its 

 dilated base and the mouth, is composed of narrow prismatic cells, 

 whose long axes are perpendicular to the surface, and which con- 

 tain granules of a yellowish-brown, or, in some specimens, of a 

 greenish colour. The endoderm of the wide basal portion of the 

 manubrium is very remarkable. It consists of a greatly vacuo- 

 lated granular protoplasm, in which every vacuole contains a dis- 

 tinct granular nucleus. These vacuoles may be regarded as re- 

 presenting the cavities of so many membraneless cells whose 

 boundaries, in consequence of the confluence of their walls, are no 

 longer obvious. This form of tissue, which may be also found in 

 the manubrium of other hydroid Medusa?, passes into that formed 

 by the prismatic cells of the rest of the manubrial endoderm. 



The radial canals consist of a thin ciliated endodermal layer 

 continued from the endoderm of the manubrium and surrounded 

 by a thicker ectoderm, which is composed of hexagonal nucleated 

 cells and continued from its ectoderm. Between the ectodermal 

 and endodermal layers is a distinct fibrillated layer, the fibres of 

 which, after accompanying the canal to the point where this 

 enters the marginal canal, here spread out on either side and lose 

 themselves in the subumbrella. Beside these longitudinal fibres, 

 the indications of a fibrillated tissue in the subumbrella are very 



