ON THE MINUTE STEUCTUEE OP STEOMATOPOEA. 187 



On the Minute Structure of Stromatopora and its Allies. By 

 Prof. H. Alletne Nicholson, F.L.S. &c., and Dr. J. Mueie, 



F.L.S. &c. 



[Eead December 20, 1877.] 

 (Plates I.-IV.) 



Intboductoey Eemaeks. 



The last decade, or thereabouts, has indeed witnessed vast changes 

 in the opinions held as to the position and relationship &c. of 

 several groups and so-called aberrant genera and species among the 

 Invertebrates. This, to a great extent, has been brought about 

 by the very considerable improvements in the modes of manipu- 

 lation, investigation, and treatment of minute structure &c., and 

 doubtless to the coordinate impetus given to the study of certain 

 hitherto obscure forms, both as to their development aad subse- 

 quent life-history. 



The forms or groups of forms which constitute the basis of the 

 present investigation have been regarded within the last fifty years 

 in the most diverse aspects. Stromatopora, even at the present 

 moment, occupies a most unsettled and uncertain position, while 

 hints and doubts flow freely as to whether it be allied to the Cal- 

 careous or the Siliceous Sponges, to the Foraminifera, to the Corals, 

 to the Hydrozoa, or to the Polyzoa, or whether it may not be a 

 heterogeneous assemblage of dissimilar forms, or perhaps the re- 

 presentative of a special and now extinct group of organisms. 

 Unfortunately the animal itself cannot be appealed to as afford- 

 ing evidence towards the solution of this problem, the remains of 

 its habitation, or its skeletal structures, alone offering data upon 

 which any judgment on this disputed point may be arrived at. 

 The object, then, of this communication is to present the results 

 of a careful examination of a large number of specimens and sec- 

 tions of different forms of Stromatopora and of related groups. 

 These results, it is hoped, will serve to throw some light upon the 

 anatomy and systematic position of the Stromatoporoids — though, as 

 a matter of course, some points have necessarily been left doubtful 

 or unsettled, to a large extent owing to the impossibility of ob- 

 taining access to many of the original specimens described by 

 earlier observers. '* 



In carrying out this investigation the materials at our disposal 

 have consisted of a very extensive suite of specimens in various 



LINN. JOUEN. — ZOOLOGY, TOL. XIV. 14 



