172 



depression. There is no trace whatever of an aboral pore such as 

 Semper describes and were it not for the fact that he carefully studied 

 living material such a structure might justly be considered an artefact. 

 The ectoderm throughout is in contact with the mesogloea and is 

 of nearly uniform character and thickness with the exception of the 

 ciliated plate. This last named structure, as the figures show, is a modi- 

 fied portion of the outer layer along the ventral surface and consists of 

 innumerable exceedingly slender cells with a height in a fully develoj)ed 



Zoanthella galapagoetisis. A, entire animal; a.b^c, regions where correspondinglj' 

 lettered sections were taken. 



condition at least twice that of the ordinary ectoderm. At its posterior 

 extremity the plate arises as a small aggregation of cells forming in 

 sections two groups, one on each side of the mid line but internally 

 separating, thus forming a distinct cleft into which the mesogloea pene- 

 trates. This condition soon ceases anteriorly where the locomotor cells 

 rapidly increase in numbers and form a layer continuous across the mid 

 line , a state of affairs persisting to the oral opening. From the figures 



