ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 189 



it constitutes the two-layered embryo. The gastral cavity arises by the 

 absorption of certain of the endoderm-cells. Then follows the swarming 

 period during which no sign of mouth or tentacles is apparent. Fixation 

 occurs by the pole which is anterior in the planula stage, and afterwards 

 mouth and tentacles arise at the opposite pole. 



Structure of Alcyonium digitatum.* — Prof. S. J. Hickson con- 

 tributes a memoir on this subject to the series in process of publication 

 by the Liverpool Marine Biological Committee. In regard to reproduc- 

 tion, Prof. Hickson's experience is that at Plymouth spawning takes 

 place only during the last fortnight of December and the first fortnight 

 of January. In the Isle of Man the time is probably later, as larvae 

 apparently of this species have been found in spring (" Easter "). The 

 memoir is based upon Prof. Hickson's previously published observations. 



Relationships of Rugose Corals, f — J. E. Duerden has been able 

 to study a series of sections of the fossil Lophophyllum proliferum in an 

 unusually fine state of preservation, and to make out the order of suc- 

 cession of the septa. He finds that, as stated by Pourtales thirty years 

 ago, this coral is primarily hexameral, not tetrameral, for there are six 

 primary septa, separated by six intcrseptal spaces. Subsequent septa 

 only appear within four of the six primary interseptal spaces, and of 

 these the larger, which are entosepta, all appear before the smaller or 

 exosepta. According to the author, the Eugosa must therefore be re- 

 garded as nearer to the Zoanthids than to any other type of Anthozoa. 

 He suggests the following arrangement to indicate the different type6 

 of metacnemic sequence now known in Actiniaria and Madreporaria, 

 and the position amongst them of Rugosa : — 



(1) The metacnemes arise as unilateral pairs at one, three, seven, &c, 

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

 one, two, three, or more cycles — 



(a) Non-skeletal. Most Actinians. 



(6) Skeleton- forming. Most recent Madreporarian corals. 



(2) The metacnemes arise as bilateral pairs at only one region within 

 two or more of the primary exocceles — 



(a) Non-skeletal. Zoanthids. 



(b) Skeleton-forming. Lophophyllum, and probably other Rugosa. 



(3) The metacnemes arise as bilateral pairs at one region within one 

 or both of the axial exocoeles — 



(a) Non-skeletal. Cerianthids. 



(6) Skeleton-forming. Porites. Madrepora. 



Position of Neostroma. % — Prof. A. Tornquist gives an account of 

 Neostroma sumatraensis sp. n., and shows that it is a mesozoic Stromato- 

 poroid, referable to the family Disjectoporidte. The three families of 

 Stromatoporoids (or Lamellataezoa) — Stromatoporidaa, Actinostromidffi, 

 and Disjectoporidse — extend far into the Mesozoic, and it is not beyond 

 the limits of possibility that living representatives may be found. Of 

 their relation to other Hydrozoa nothing can be safely said. 



* Proc. and Trans. Liverpool Biol. Boo., xv. (1901) pp. 92-113 (2 pie.). 

 t Johns Hopkins Univ. Circ, xxi. (1902) pp. 19-25 (12 figs ). 

 J SB. Preuss. Akad., 1901, pp. 1115-23 (5 figs.). 



