438 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of the corallum displays the median dark lines of six primary septa, 

 separated by six interseptal spaces. There is no doubt as to the primary 

 hexameral character. 



" So far as Lophophyllum can be taken as a representative, the 

 peculiar septal plan of the Rugosa introduces no new conception into 

 Anthozoan studies, and any other peculiar features which the order 

 possesses, such as tabulas and vesicular endotheca, are of very sub- 

 ordinate morphological importance compared with the septal scheme." 



If the manner of mesenterial development be taken as the index of 

 natural relationships, the bilateral Zoanthids, primarily hexameral, but 

 with their metacnemic development restricted to two exocoelic regions, 

 are, more than any other Anthozoan type, the modern representatives of 

 the Rugosa. 



The following arrangement indicates the different fundamental types 

 of metacnemic sequence now known within the Actiniaria and Madre- 

 poraria, and the position amongst them of the Eugosa. With the 

 •exception of the Cerianthea? all possess a primary hexameral stage, 

 consisting of six pairs of mesenteries with six primary entocoelic 

 chambers and six primary exocoelic chambers. Calcareous septa may 

 appear within only one or in both series of chambers. It is in the suc- 

 cession of the later mesenteries and septa — metacnemes and metasepta — 

 that the divergences are introduced. 



I. The metacnemes arise as unilateral pairs at one, three, seven, &c. 

 regions within all the six primary exocceles, and become arranged in 

 one, two, three, or more cycles : — 



(a) Non-skeletal. (b) Skeleton-forming. 



Most Actinians. Most recent Madre- 



porarian corals. 



II. The metacnemes arise as bilateral pairs at only one region with- 

 in two or more of the primary exocceles : — 



(a) Non-skeletal. (fc) Skeleton-forming. 



Zoanthids. Lophophyllum and pro- 



bably other Kugosa. 



III. The metacnemes arise as bilateral pairs at one region within 

 one or both of the axial entocceles : — 



(a) Non-skeletal. (6) Skeleton-forming. 



Cerianthids. Porites, Madrepora. 



Protozoa. 



Conjugation of Dendrocometes paradoxus.* — S. J. Hickson, assisted 

 by J. T. Wadsworth, has made a study of conjugation of this Acinetarian 

 which commonly oocurs on the gills of Gammarus pulex. The phenomena 

 may be briefly stated as follows : — Two individuals in proximity on a 

 gill of Gammarus send out simultaneously blunt lobe-like processes, 

 which may be called the conjugative processes. These meet but do not 

 completely fuse, a distinct membrane delimiting the process of each 

 individual throughout the conjugation. This membrane does not pre- 

 vent the fusion of the meganuclei nor of the conjugative micronuclei in 



* Quart. Journ. Micr. Sci., xlv. (1902) pp. 325-62 (2 pis.). 



