136 



PROF. G. J. ALLMAN ON LIMNOCODIUM VICTORIA. 



indistinct — a condition which contrasts strongly with the highly- 

 developed musculature of the subumbrella in the Trachomedusae, 

 The velum is composed of two layers of nucleated cells having 

 between them an annular layer of muscular fibres ; while between 

 the muscular layer and the lower or abumbral cellular layer are 

 the marginal vesicles, with their caudal extensions running from 

 the attached to the free edge of the membrane. 



Fig. 3. 



Part of tlie margin, enlarged. 



mmm, thickened and sinuated margin ; v v, velum ; I, I, I, lithe-cysts ; r, radial 

 canal ; c c, circular canal ; n, nerve-ring. 



The reproductive elements are developed between the endoder- 

 mal layer (spadix) of the sporosac and its ectodermal layer. I 

 believe they take their origin in cells of the endoderm. After a 

 sporosac has become naturally emptied of its contents, it will be 

 found that the space which these had occupied between the 

 endoderm and ectoderm is now traversed by irregular bands of 

 granular protoplasm, which extend from the walls of the spadix 

 internally to the ectoderm externally, being attached by their ends 

 to both these membranes. Some of these bands are simple, others 

 branched. They present here and there fusiform enlargements 

 irregularly distributed along their length. 



In many instances a thin layer of clear spherical cells may be 

 seen still closely adhering to the spadix. These I regard as the 

 remains of the spermatogenic tissue ; and their intimate relation 

 with the walls of the spadix, while they are separated by a wide 



