ZOOLOGY AND BOTANY, MICROSCOPY, ETO. 



647 



Ccelenterata. 



Revision of British Actiniae.* — Prof. A. C. Haclclon has publishrcl 

 the lirst part of ca rev siou of Br.tish Actinians ; in this he deals with 

 the Sagartidfe, tlie Eilwardsiidae, the Halcampidee, and the Zoantliete. 

 The general conclusions to which his work has led him may be thus 

 summed up. In larval Ai;tinife two mesenteries arise at right angles to 

 the lung axis «if tlie oesoi^hagus, and divide the archenterou into two 

 cliambers. A pair of mesenteries appear in the larger of the two 

 primitive chambers ; a third pair is developed in the smaller of the two 

 piimitive chambers, and immediately afterwards another pair of mesen- 

 teries ajjpear. A short resting static now occurs, in which eight 

 mesenteries are alone present, and thy corresponding chamhers are 

 produced into eight tentacles. This appears to be a characteristic 

 phase in the development of all the Actiniae hitherto studied, with the 

 exception of Cerianthus. There is reason for believing that in most, if 

 not all. these eight mesenteries are homologous w.th those of the 

 Edwardsije ; in other words, such forms as Halcampa, Actinia, Cereiis, 

 and Bunodes, if not all other sea-anemones (except Cerianthus) pass 

 through a larval stage which is permanently retained in the adult 

 Edwardsife. 



The next stage is characterized by the practically simultaneous 

 development of two pairs of mesenteries ; these for some time remain 

 imperfect. The fifth and sixth pairs next reach the oesophagus, and 

 constitute the ground or fundamental form of the typical hexamerous 

 Actiniae. Halcampus clavus of R. Hertwig does not advance further. 



A pair of small mesenteries, with their longitudinal muscles facing 

 one another, is developed in each exocoele ; this is almost the permanent 



* Sci. Trans. R. Dublin Soc., iv. (1889) pp. 297-361 (7 pis.). 



