ACTINOLOGICAL STUDIES. 213 



any knowledge of their anatomy." The great importance 

 and necessity of a work of this character is then apparent, 

 and it is the unfeigned regret of all workers in this group 

 of animals that Prof. Haddon has not completed this 

 revision. 



The principal morphological characters of the Hexac- 

 tinioe are the hexamerous arrangement of the mesenteries 

 in pairs and the presence of two " oesophageal grooves " — 

 the " siphonoglyphs ' of some authors — associated with 

 two pairs of " directive ' mesenteries. But a large 

 amount of variation from this typical condition has been 

 shown to exist in a number of species, both in the 

 arrangement of the mesenteries and in the number of 

 oesophageal grooves and directive mesenteries. It is, 

 therefore, of the greatest importance that not only should 

 there be a thorough knowledge gained of the anatomy of 

 these animals, but that that knowledge should be founded 

 on the examination, where possible, of a large number of 

 specimens, so as to prevent the possibility of mistaking 

 individual variations for characteristics of the species. It 

 is only by this means, in view of the amount of variation 

 shown to exist, that a true and faithful estimate can be 

 formed of the morphological and phylogenetic value of 

 the various anatomical characters. 



Acting on the kind suggestion of Prof. Herdman, to 

 whom I wish to record my sincere thanks for much 

 valuable advice and active interest in the work, I have 

 commenced a series of observations on the various 

 species of Actinians found in this neighbourhood. It is 

 my intention to take them in rotation, and examine a large 

 number of specimens of each species, in order to determine 

 the constancy or otherwise of the different points of 

 their anatomy. This, my first contribution, deals with 

 the well-known species, Actinia equina, Linn. — the 



