FUNCTION OF ACANTHOPORES 363 



ACANTHOPORES 



The function of acanthopores has long been a puzzle. It has been 

 surmised that these hollow, thick-walled tubules were in the living colony 

 surmounted at the surface by some sort of spine, aviculariuni or vibrac- 

 ulum. Waagen and Wentzel (36) made the mistake of supposing that 

 they were young zowcia (corallites) . Several years ago we noticed among 

 our sections of Del-ayia niaculata a few examples of overgrowths in which 

 the entire spine, extending well above the surface of the zoarium, is 

 preserved. Two of these sections are figured herewith (figures 51 and 

 52). In figure 51 every detail of the overgrowth, calcite structure and 

 all, has been delineated, in order to eliminate, so far as possible, the 

 personal interpretations of the authors. The drawing is photographically 

 exact. The appearance at t, which might almost be interpreted as an 

 avicularium, has probably been produced by the crushing of the end of 

 the spine. The spine shown in figure 53 extended up into a mass of 

 sediment that had coated the zoarium and had subsequently been covered 

 by the overgrowth. It seems to be perfectly intact. The actual diameter 

 of these spines is about that of a human hair and they extend about 21/^ 

 zooecial diameters above the zoarium. Most acanthopores, however, were 

 much smaller than these. In Del-aijia the exsert portion of the spine 

 was brittle, as shown by the fact that in overgrowths of specimens of 

 (his genus quantities of shaiply broken fragments of spines are often 

 seen. A bent spine is a rare occurrence. There is some evidence, how- 

 ever, that in certain other genera the spines were flexible (10). The 

 laminffi of which the spine is composed run parallel with the axis of the 

 spine. Their appearance under high magnification is shown in figure 

 53. This drawing is from the region s of the preceding figures. Figure 

 51 shows the region s' of a spine highly magnified. This part of the 

 spine has been buttressed by extensive secondary deposits laid on it by 

 the adjoining zooecia. The primary wall of the spine can be distinguished 

 in the inner fascicle of laminae next to the lumen. In figure 51 this pri- 

 mary spine can bo traced far down into the zoarium. It is obvious that 

 as the zocecia grow distally they submerge the exsert portion of the spine, 

 whicli latter keeps lengthening. If the axis of the spine is not perfectly 

 parallel with the axes of the surrounding zofBcia, the submerged portion 

 of the acanthopore will trend more or less diagonally between adjoining 

 zooecial walls. This explains an appearance very often seen in longi- 

 tudinal sections of species that have large and well defined acanthopores. 



The protective function of such spines can scarcely be doubted. Their 

 very number and relation to the zorecial apertures indicate sucli a function 



