ZOOIDAL TUBES. 49 



skeleton in Labechia could be truly alive, the ccenosarcal sheet and its zooids being 

 superior to the last-formed series of " tabulce." Observations made upon such 

 species of Labechia as L. alveolaris, n. sp., of the Wenlock Limestone, and 

 L. serotina, n. sp., of the Devonian (Fig. 4), would strongly confirm the view here 

 taken as to the tabular nature of the connecting-processes in the genus Labechia. 

 It is quite certain, at any rate, that no differences whatever can be detected in 

 thin sections between the connecting-processes in the species of Labechia just 

 mentioned,' and the "tabula?" of such Corals as Favosites and Alveolites. 



(e) Zooidal Tubes. — The great difficulty which many observers have felt in the way 

 of accepting the reference of the Stromatoporoids to the Coelenterata is that no clear 

 demonstration had been made of the existence in the skeleton of any tubes which 

 might have lodged the zooids of a Hydrozoan or Actinozoan colony. It was this 

 difficulty which induced me previously to adhere to the reference of the group to the 

 Bhizopoda. The first steps in the removal of this difficulty were taken by Carter in 

 his researches on Hydractinia ; but, after all, the thin crust of Hydractinia is in many 

 respects very different to the huge masses of the larger Stromatoporoids, and it 

 seemed only reasonable to expect that the latter, if Ccelenterate, ought to show in 

 their skeleton traces of tubes, such as might have been inhabited by separate zooids. 

 Many observers have regarded the radial pillars as hollow, and as being such 

 zooidal tubes ; but it is, I think, quite certain that this view is untenable. Even 

 when hollow, the radial pillars seem to be mostly closed superficially ; and where 

 it may be surmised that they did open on the surface (as, perhaps, in Henaatostroma 

 Schliiteri, Nich.), it still seems certain that they did not lodge zooids, the cavities 

 for which can, indeed, be shown to exist elsewhere. Such cases can, in fact, be 

 parallelled by what we see in Hydractinia circumvestiens, Wood (Plate VI, figs. 8 and 

 9), in which definite zooidal tubes coexist with large perforated pillars. 



The most complete demonstration of the existence of definite zooidal tubes is 

 obtained from the examination of the skeleton of the genus Stromatopora, 1 Goldf., 

 and of those allied types which make up the " Milleporoid " section of the Stroma- 

 toporoids. In these forms the skeleton is essentially composed of vermiculate and 

 reticulated calcareous fibres, forming a more or less continuous framework, which 

 is only roughly and imperfectly divisible into radial and concentric elements. The 

 skeleton has in fact a close general resemblance to that of the recent Mill&pora, except 

 that the tubes which traverse it are, as a rule at any rate, not divisible into two distinct 

 series, differing from one another in point of size. The skeleton in these forms is, 

 however, penetrated by numerous minute, flexuous, but essentially parallel, vertical 

 tubes (Plate V, figs. 10,13 and 15), which are not bounded by definite walls but are 



1 It must not be forgotten that the forms understood here under the name of Stromatopora are 

 those of the type of the true Stromatopora concentrica, Goldf., and are therefore wholly distinct from 

 those which have usually been grouped under Stromatopora. 



