CH^ETETID.E AND MONTICULIPORID.E. 257 



nor are any traces of transverse partitions or " tabula; " to be 

 detected. Between the true cells, and more or less completely 

 separating them from one another, are numerous smaller " in- 



Fig. 34. —A, Fragment of an undesciibed living species oi Hctcropoi-a, from New Zealand, of 

 the natural size ; and )), Surface of the same, enlarged (original) ; c. Surface of a branch 

 oi Hefcropora sjth'dkulaia, from the Tertiary, enlarged (after Reuss). 



terstitial tubes," which in this particular form appear to have 

 their mouths unrestricted by any partial diaphragm, and which 

 nearly equal the true cells in point of size. It is the presence 

 of these interstitial tubes which gives to Hderopora its very 

 close superficial resemblance to the ramose species of Monti- 

 culipora and Fistidipora. Not only is the nature of these 

 tubuli still obscure, but they present the curious feature that 

 they exhibit (in some cases at any rate) structures which, to 

 say the least of it, admit of comparison with the " tabulae " of 

 Monticulipora. Many or all, namely, of the mouths of the 

 " interstitial tubes " of some species of Heteropora are closed 

 by a delicate transverse partition or lid, which is perforated in 

 its centre by a small aperture, and is placed a little below the 

 lip of the opening. Sometimes these " hymen-like lids," as 

 shown by Prof. Busk, are periodically produced at successive 

 stages of erowth, and thus come to simulate " tabulae." In 

 Heteropoi-a clavata, Goldf , the same distinguished observer has 

 also shown that the mouths of the interstitial tubes commonly 

 exhibit a stellate appearance, owing to the projection into their 

 interior of delicate vertical lamcllce, which simulate the " septa " 

 of the true coi'als. 



R 



