ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 543 



Septa and Mesenteries of Madreporaria. * — S. E. Duerden has 

 studied the disputed questions connected with the order of the appearance 

 of septa aud mesenteries in living and preserved specimens of certain 

 West Indian forms. He finds that the first six pairs of mesenteries 

 differ so much in their mode of origin and significance from the others 

 as to deserve a special name. He therefore calls them protocnemes, and 

 the subsequently developed ones metacnemes, the associated septa being 

 protosepta and metasepta. He finds that in Manicina areolata the 

 twelve protocnemes arise in bilateral pairs in a definite order, which is 

 probably the same throughout the Madreporaria and Actiniaria ; two 

 pairs of directives are always present ; the first four pairs of proto- 

 cnemes are the earliest to unite with the stomodaaum, and a long interval 

 may elapse before the fifth and sixth pairs become complete and the 

 metacnemes appear ; the development of the protocnemes in asexually 

 produced buds is in close agreement with that of sexually produced 

 polypes; most of the polypes of the genera Madrepora and Porites 

 never pass beyond the protocnemic stage. With regard to the meta- 

 cnemes the results are stated as follows. In most coral polypes the 

 addition of mesenteries beyond the primary six pairs always takes place 

 in successive unilateral pairs, the corresponding pairs on each side 

 being usually simultaneous and always exocoelic ; the first cycle of 

 metacnemes (six pairs) arises in successive pairs from one aspect of the 

 polype (sulcar or ventral) to the other (sulcular or dorsal), the pairs 

 afterwards becoming equal ; the second cycle consists of twelve pairs, 

 of which six arise in succession from one aspect of the polype to the 

 other, and all on the same aspect of the first-cycle metacnemes ; the re- 

 maining six pairs appear in the same succession but on the reverse 

 aspect. In Porites the additions of mesenteries beyond the six primary 

 pairs take place in bilateral pairs in only one region and within one 

 enterocoele, the mesenteries remain unicyclic, and the unilateral pairs 

 beneath the stomodasum consist of alternately longer and shorter me- 

 senteries. In these respects the metacnemes of Porites differ from those 

 of all other known coral polypes. In Actiniaria the metacnemes in the 

 Hoxactiniae are similar to those of most Madreporaria ; those of 

 Zoantheae approach somewhat to the conditions seen in Porites, while 

 those of Ceriantheas resemble those of Porites very closely. It would 

 seem, therefore, that Porites bears the same relation to the other Madre- 

 poraria as Cerianthus does to the other Actinaria. In Porites both 

 metacnemes and metasepta arise in the same manner as in many of the 

 extinct Palaeozoic corals. All the evidence seems to show that the 

 protoseptal phase has always been hexameral in the Zoantharia, and 

 that it is only with the metasepta that the distinctive characters — 

 cyclical or bilateral — truly commence. The author considers that the 

 arrangement of the septa and mesenteries on the cyclical or bilateral 

 plan should constitute the basis for a primary sub-division of corals. 



Madreporaria from the Sandwich Islands and Samoa, f — Prof. Th. 

 Studer comments on the fact that, while in the Central Pacific the 

 Madrepores and most of the Astrseidae reach their northern limit, in 



* Circ. Johns Hopkins Univ., xix. (1900) pp. 47-53 (12 figs.). 

 t Zool. Jahrb., xiv. (1901) pp. 388-428 (9 pis.). 



