GENUS IDIOSTROMA. 103 



I sluill subsequently illustrate and describe the singular structures just alluded 

 to more fully, but there are one or two general considerations which may be 

 noticed here. It will be evident, namely, from the above description, that the 

 tubes in question are in most respects identical with the tubes which occur in- those 

 Stromatoporoids which have been referred to the so-called genera " Caunopora" 

 Phill., and " Viapora" Barg. In fact, the specimens would, in an ordinary way, 

 be certainly regarded as belonging to a species of Caunopora. The tubes of 

 Idiostroma oculatum resemble the embedded tubes of " Caunopora " and " Diapora " 

 in opening on the surface by large prominent apertures, in having thickened walls, 

 and in being intersected internally by tabulas. They differ, however, from the 

 tubes of " Caunopora " in the fact that the thickened wall seems to be confined to 

 the outer portion of each tube, where it begins to approach the surface, and also 

 in the important feature that the tubes to all appearance communicate freely 

 internally with the interlaminar spaces of the skeleton — a communication which 

 has not been proved to take place in the case of the tubes of " Caunopora" and 

 which probably does not take place in the latter. Leaving the nature of " Cauno- 

 pora " and "Diapora " for future consideration, it may be well to point out here 

 the grounds for thinking that the embedded tubes of Idiostroma oculatum are 

 certainly parts of the organism in which they are found ; and there are two principal 

 reasons for coming to this conclusion. In the first place, these tubes can hardly 

 belong to any organism foreign to the Stromatoporoid in which tfeey occur, seeing 

 that they appear to be to a large extent bounded only by the proper skeletal tissue 

 of the latter, while they seem clearly to open internally into the general cavities of 

 the coenosteum in which they are embedded. In the second place it is apparently 

 inconceivable that the tubes of any Coral, such as Aulopora or Syringopora, could 

 be embedded, parasitically or commensally, throughout the numerous slender and 

 branching stems of Idiostroma oculatum in such a way that the mouths of the 

 tubes, and the mouths only, should appear at the surface. If, indeed, we could 

 remove the enveloping skeletal tissue of Idiostroma oculatum, and could inspect 

 the embedded tubes alone, we should find a structure entirely unlike any known 

 species of Auloporoid or Syringoporoid Corals. Moreover, the main axial tabulate 

 tube of I. oculatum is, beyond all question, a part of the Stromatoporoid, and it is 

 only close to the surface that the radial tubes exhibit any feature which would 

 distinguish them from the axial tube, since it is only in this region that they appear 

 to develop proper walls. 



If we accept the conclusion that the radial tubes of I. oculatum belong to the 

 organism in which they are found, it still remains to consider what these tubes 

 are, and what functions we may suppose them to have discharged. As regards this 

 point, it is to be observed, in the first place, that some specimens of Idiostroma 

 oculatum, though possessing the axial tubes in the stems, show no traces of the 



