ACTINOLOGICAL STUDIES. 307 



three pairs and one with four pairs. Hence it is seen 

 that in many species uniformity in the number of oesopha- 

 geal grooves is by no means characteristic. 



As before mentioned, in Actinia equina all the seven 

 variations which occurred among the 165 specimens ex- 

 amined were in the arrangement and number of the 

 oesophageal grooves. In four specimens a single oesopha- 

 geal groove only existed, in one specimen three existed, 

 and in two specimens two oesophageal grooves w T ere 

 present, but were not arranged opposite each other as in 

 the normal condition. It will be noticed that a decrease 

 in the number is more common than an increase, and 

 this is in accordance with the records of other investi- 

 gators, and to which McMurrich draws attention in his 

 paper on Sagartia spongicola (1897, p. 116). 



Of the four specimens with the single oesophageal 

 groove, two had tw T o cycles of mesenteries complete (1 

 pair of directives, 11 pairs of non-directives) ; one had 

 the primaries alone complete (1 pair directives, 5 pairs 

 non-directives) ; and the remaining one had the primaries 

 and four of the secondaries complete (1 pair directives, 9 

 pairs non-directives), the two remaining pairs of mesen- 

 teries of the second cycle being incomplete. This last 

 condition is shown diagrammatically in PI. XX., fig. 2. 

 (In the diagrammatic figs. 2, 3, 4, and 5, the primary and 

 secondary mesenteries only are shown). 



The specimens possessing three oesophageal grooves 

 exhibited perfect hexamerism like all the others, and 

 possessed twelve complete mesenteries (3 pairs directives 

 (cZ.), 9 pairs non-directives (?i. cl.), see PL XX., fig. 3). Of 

 the three oesophageal grooves (ce. g.), two occupied the 

 normal position opposite each other. 



The third type of variation, found in the two specimens 

 in which the two oesophageal grooves present were not 



