204 J. H. ASH WORTH. 



with each other. Very close to the base of attachment of the 

 colony, a canal may usually be seen passing from each side of the 

 lowest portion of each primary coelenteron, so that in longitudinal 

 section the coelenteron and its two canals appear j_-shaped. The canal 

 opens into the base of a neighbouring coelenteron. These canals are 

 probably the representatives of the original stolon from which all the 

 primary coelentera grow out. 



The well-developed longitudinal canals running parallel to and 

 between the coelentera of the polyps of Xenla remind one of the 

 coenenchymal tubes of Hello pora ccerulect, described by Moseley (1881) 

 and by Bourne (1895). The resemblance is more striking when we 

 consider that in both cases the longitudinal tubes are lined by endo- 

 derm, and are connected near the upper surface of the colony with a 

 network of superficial endodermic canals. 



The differences between the canals of Xenia and the coenenchymal 

 tubes of Heliopora are chiefly due to the fact that in the latter only 

 the outer portion of the coral is living, the internal parts consisting of 

 calcareous skeleton only, whereas in Xenia the whole colony is pene- 

 trated by living cells. In Heliopora, therefore, the coelentera of the 

 polyps and all canals running into the colony must terminate within 

 about 2 mm. of the surface, as this is the lowest limit of the living 

 substance. The coenenchymal tubes of Heliopora have an exactly 

 similar course to the longitudinal canals of Xenia, as they run parallel 

 to the coelentera from their point of origin from the superficial canal 

 system (just beneath the ectoderm covering the free surface) to the base 

 of the living portion of the colony, where they and the coelentera 

 terminate blindly. 



Moseley (1881) believed the coenenchymal tubes of Heliopora to be 

 degenerate siphonozooids from which the mesenteries had disappeared, 

 but Bourne (1895) has shown that they cannot be so regarded. 



In order to find a parallel to these coenenchymal tubes of Heliopora, 

 Bourne thought it necessary to go outside the Alcyonaria and compare 

 the tubes with certain longitudinal canals of Millepora, described by 

 Moseley (187G). After carefully studying the canal system of Xenia, it 

 appears to me that tins course is not now necessary, as the comparisons 

 instituted above between the coenenchymal tubes of Heliopora and the 

 longitudinal canals of Xenia are perfectly justifiable. It is true the 

 coenenchymal tubes of Heliopora are more numerous than the longitu- 



