246 



HARBWICKE'S SCIENCE-GOSSIP. 



foliaceous, and the " cells are in two layers parted by 

 a calcareous septum and opening on both surfaces." * 

 In the "Ann. and Mag. of Nat. Hist," vol. xiii., 

 Mr. Wood had called the same species Diasiopora 

 nieandriua, but in this species Mr. Busk draws atten- 

 tion to a remarkable feature when he says, "As in 

 several other Cyclostomata, more especially of those 

 belonging to the present family, the mouths of the 

 tubes in this species are eventually closed with a 

 calcareous lid, having usually a minute central perfo- 

 ration." t In the "Crag Polyzoa " Mesenteiipora was 

 placed in the family Tubuliporidre, whereas in the 

 Cyclostomata of the same author it was placed as the 

 second genus of the family Diastoporidce. Mr. Hincks 

 in his Brit. Marine Polyzoa disallows either the 

 family Diastoporidae, or the separation as a genus 

 the Mesenteripora ; he places in one family — the 

 Tubuliporidce — as Diastopora whether they be dis- 

 coidal expansive, or foliaceous, [and all that he 

 troubles himself with is the character of the cell. 

 In his justification of this judicious course, speaking 

 of the genus Porella, Gray, Mr. Hincks says,J " Un- 

 less we are content with the old and (certainly very 

 simple) method of lumping all erect forms together, 

 without any reference whatever to the cell, we have 

 only a choice between these two courses, to found 

 genera for the variations of growth as well as for the 

 more important modifications of cell in each family, 

 or to make the zocecium (cell) the basis of the genus 

 and treat the ordinary variations of habit subsection- 

 ally." In deference to an opinion like this, it will be 

 necessary to spend some little thought upon Polyzoa 

 cells in general, but on the cells of the Diastoporidse 

 in particular. 



A cell is one of the most typical elements in the 

 zoarium of a Polyzoon ; so much so, that it has been 

 accepted as a base on which the classification of a 

 very large group of Polyzoa may safely rest. There 

 is constancy in the character of the orifice, and ac- 

 cording to their arrangement— the endosarcal passages 

 in their sides and ends, end also according to the 

 shape — incurvation or expansion of the lips of the 

 orifice, so the greater may be broken up into smaller 

 groups or genera. This is one of the chief charms of 

 the Rev. Thomas Hincks's classification in his work 

 on British Marine Polyzoa. Whenever we are deal- 

 ing with a group like the Cheilostomata, the impor- 

 tance of an arrangement like this cannot be over- 

 estimated. But even here there is one small cluster 



small comparatively— that will not yield to this mode 

 of dealing with them. This cluster is the Cellepora, 

 and whether we are dealing with British, Foreign, or 

 Fossil species, the difficulties are much increased 

 whenever we recede backwards in time. While we 

 are dealing with recent species there are elements of 

 structure in the cell that we may rely upon for a classi- 



• P- 109- t Ibid., p. no. 



I ' Ann. Mag. Nat. Hist.," Feb. 1879, p. 160. 



ficatory purpose. These are the Chitinous organs 

 or the opercula which serve the purpose of lids, or, 

 in other words, of oral valves of the cells. In the 

 Cyclostomata there is ver}' little that may be relied 

 upon as a valid test in the cells, especially in the 

 early stages of a colony. We must therefore base 

 our observations on the early, as well] as on later 

 stages, before we can pronounce positively that a 

 primary cell disassociated would have developed 

 into a Stomatopora or into a Diastopora. Yet there 

 are elements even here, which, if closely followed, 

 will betray the character of the future colony, proxi- 

 mately, if not positively. In Diastopora, the primary 

 cell very early takes up a proper position in the 

 zoarium. It is not always central, but it soon adapts 

 itself to the exigencies of its position so as to compel 

 (I do not mean intellectually compel) all the other 

 cells to assume first a flabellate and ultimately a 

 circular arrangement around it. I have before me 

 an Oolitic Terebratula, and one of its valves is'par- 

 tially covered with numerous colonies of a proliferous 

 Diastopora. Many of the circular patches send out 

 a strong primary cell, and very soon a development 

 takes place by gemmation which assumes the forms 

 already indicated. On the Terebratula there are no 

 fewer than fifty colonies which can be conveniently 

 studied for habit alone. As in the fossil, so in recent 

 types' of Diastopora, with a somewhat constant and 

 peculiar habit — not essentially so — there is found a 

 pretty constant type of cell. It is similarly so in the 

 Foliaceous Diastopora, or the Mesenteripora of 

 Blainville and Busk. It is very true that this last 

 genus often appears in its earlier stages sometimes 

 as a circular, sometimes as a branching, and some- 

 times as a bilamellate form. Yet those who have 

 closely studied the Oolitic types — the crag types I 

 have not been able to study except from the figures 

 in Professor Busk's " Polyzoa " — will soon see that 

 the type of cell in the early, or encrusting stages of 

 Mesenteripora, are very different from the more 

 rounded and less connate types of the Diastopora cell.* 

 Take the three types of the one species, Mesenteripora 

 vieandrina, t given by Busk, and we see at a glance 

 that the cells of this type differ from the cells of 

 ordinary Diastopora. Here the cells are contiguous, 

 sometimes rounded or flattened, and sometimes con- 

 nected, only apparently so by the cell walls. The 

 distal part of the cells is rarely produced as in Dia- 

 topora ; but we must not push this character too far, 

 for I have met with examples of specimens that may 

 be placed with INIesenteripora or Diastopora indiffer- 

 ently, some of whose cells are produced. It will be 

 well, therefore, in consideration of the difl'iculties 

 surrounding these types, to keep them divided, but 



* I am not in the position, from the want of proper material, 

 to revii-e the Oolitic Mesenteripora, but I very strongly suspect 

 that sotne of these will have to be passed over to the Cheilo- 

 stomata. The types of the cells in some species are unlike 

 ordinary Diastopora cells. 



f Plates xvii., xviii., and xx. of " Crag Polyzoa." 



