64 BRITISH STROMATOPOROIDS. 



adventitious or imbedded structures of any kind. It is necessarily impossible to 

 speak with certainty as to tlieir nature ; but the most probable hypothesis seems 

 to be that which would regard them as having lodged the reproductive zooids, and 

 as corresponding with the " ampulla? " of the Stylasteridw and of Millepora 

 Murrayi, Quelch. It may, further, be conjectured, with some probability, that the 

 axial tubes of the cylindrical types of Idiostroma (PL IX, figs. 6, 7, 8), as 

 also of StacJiyodes (PI. VIII, fig. 10), with their lateral tabulate offshoots, were 

 connected with the development of the reproductive zooids. 



III. SYSTEMATIC POSITION AND AFFINITIES. 



The Stromatoporoids have been referred by different naturalists to very dif- 

 ferent groups in the animal kingdom, but most generally to one or other of the 

 four divisions of the Sponges, to the Foraminifera, the Corals, or the Hydrozoa. "We 

 may, therefore, speaking roughly, say that they have been generally regarded either 

 as Rhizopods or Coelenterates. The former view is the one which, with some 

 reservations, I have myself held, being influenced in so doing principally by the 

 fact that no observer had succeeded in demonstrating in any Stromatoporoid (ex- 

 cluding the problematical forms grouped under Caunopora, Phill.) the existence of 

 any tubes or cells which might have been supposed to have served for the lodg- 

 ment of the zooids of a Coelenterate colony. My own researches, however, have 

 now led me to recognise the presence of such unquestionable zooidal tubes (as pre- 

 viously described) in various typical Stromatoporoids, and I am therefore, now able 

 to frankly accept the views of Carter, Lindstrom, Steinmann, Zittel, Bargatzky, 

 and other well-known observers, as to their Coelenterate affinities. I am also quite 

 satisfied that the Stromatoporoids belong to the Hydrozoa and not to the Actinozoa, 

 and that they have relationships with both Hydractinia on the one hand and Mille- 

 pora on the other hand, though I regard them as quite distinct from either of these 

 genera, and as forming a special group of the Hydrozoa, for which the name of 

 Stromatoporoidea, originally proposed by Dr. Murie and myself, may be retained. 



In the presence of the large body of evidence which we now have as to the 

 minute structure of the Stromatoporoids, it does not appear to me to be necessary 

 here to discuss in detail the reasons which induced different investigators to refer 

 the Stromatoporoids to the Foraminifera, 1 the Sponges, or the Corals. I shall, 



1 From one point of view, the system of minute tubuli which I have been able to show to exist 

 within the skeletal tissue of many Stromatoporoids might, no doubt, be accepted as evidence of Foram- 

 iniferal affinities. The value of such evidence is, however, destroyed by the still closer resemblance 

 of the tubuli in question to the minute canaliculi of the skeleton in various of the Hydrocorallines {e.g. 

 Distichopora and AUopora). 



