ZOOLOGY OF THE BERMUDAS. 125 



elevations of the mesogloea. This tissue throughout the 

 column is very thick, measuring on the average 1 mm. in 

 thickness. It presents numerous anastomosing canals filled 

 with cells, as well as the delicate canals which have been de- 

 scribed by Erdmann and others, very distinctly. These canals 

 are without doubt processes from the large canals, and the 

 structure of the zoaiithan mesogloea may be compared to that 

 of a bone, such as a frog's femur, the anastomosing canals 

 being compared to the lacuna, and the delicate canals to the 

 canaliculi. My preparations of M. tuberculata seem to show 

 that the lacunae arise from both the ectoderm and the en do- 

 derm. In some of my sections deep bays can be seen running 

 from the endoderm up into the mesogloea, and from their ends 

 and sides numerous canaliculi can be seen branching out. 

 These bays are found in various stages of enclosure by the 

 mesogloea, the cells which they contain being in some cases 

 continuous with the general endoderm, in other cases almost 

 separated from it, and finally quite so. So too with the ecto- 

 derm. The lacuna} which have just been formed in this man- 

 ner are much larger than the majority of those scattered 

 through the mesogloea, these frequently consisting of only a 

 few cells or even a single cell, and further, the newly-formed 

 lacunse usually contain zooxanthelke, which are rare in the 

 older ones. It would seem as if many of the newly-formed 

 lacuna become divided into smaller portions which separate 

 from each other, except by the delicate canaliculi, and at the 

 same time undergo an alteration in the histological structure 

 of their cells, the zooxanthellre disappearing, and the cells be- 

 coming filled with refractive, deeply-staining granules. It 

 seems not improbable that these altered cells are concerned in 

 the formation of the mesogloea, their granules being particles 

 which will later on be added to the matrix of the mesogloea. 



Upon the outside of the column is a thin cuticle (PL 11, fig. 

 6, cu) similar to what occurs in Z. sociatus and Z. flos-marinus. 

 Andres* considers this to be merely a differentiation or hard-. 



* A. Andres. On a new genus and specie^ ol Zoamhina iM.ilacoilennata (Pan 

 ceria s/>ongiosa, sp. n.) Quart. Journ. Micros. Sci. N. S. Vol xvii. 1887. 



