124 THE VOYAGE OF H.M.S. CHALLENGER. 



are in Heliopora, and to have been most variable in number, but often twelve, as also in 

 Heliopora. Milne-Edwards describes from ten to twelve septa in Favosites gothlandica. 

 In Michelinia favosa thirty to forty subequal septal strise are to be made out at the 

 upper margin of the wall of the calicle. It seems not unlikely that the septa in the 

 Favositidse were pseudo-septa as in Heliopora, and that these coralla were formed by 

 Alcyonarians, the perforations in the walls having transmitted transverse canals of soft 

 tissue like those of Heliopora and Sarcophyton, and the coralla being free of tubular 

 coenenchym, because none of the polyps were aborted as in Heliopora. Some Favositidse 

 seem to have formed a compound colony, consisting of autozooids and siphonozooids, for 

 example, Favosites forhesi, in which a few large cells are seen set amongst numerous 

 surrounding small ones. Heliolites seems to a certain extent to form a transition stage 

 between a condition such as that in Favosites forbesi and the condition in Heliopora ; 

 for in Heliolites, the more ancient form, the coenenchymal tubes are regularly hexagonal, 

 and apparently much more nearly equal in breadth to the calicles than in Heliopora. 

 In the growing points of Heliopora the hard parts are made up of a series of open often 

 hexagonal tubes, and resemble Favosites in their surface aspect. In Heliopora the 

 transverse canals pass over notches in the summits of the walls of the coenenchymal tubes 

 and calicles, in order to place these cavities in communication with one another. In 

 Favosites the calcareous tissue surrounded the transverse canals, and the perforations in 

 the walls of the calicles were thus produced. 



If Favosites was an Alcyonarian, Chatetes was of course also of that group. The 

 genus Alveolites amongst the Favositidse is peculiar for the possession of three tooth-like 

 prominences as the only representatives of septa. One tooth, well developed, is situate 

 inside the calicle ; on that side of each calicle which lies externally in the colony, and 

 opposed to this on the tip of the calicle next the interior of the colony, are a pair of 

 rudimentary teeth. This arrangement reminds us at once of the distinction of dorsal and 

 ventral mesenterial interspaces in Alcyonarians, and the direction of all the " Dorsalfacher " 

 in Sarcophyton aud Heliopora towards the central axis of the colony. Iu Alveolites the. 

 two teeth seem to correspond to the " Dorsalfach," and the single one to the " Ventral- 

 fach," the two teeth having occupied the space devoid of retractor muscles. Kolliker 

 describes a series of teeth as existing at the margin of the calicle in Renilla, which follow 

 a constant law in their relation to the septa. When only one tooth is present it is 

 opposite the " Dorsalfach ; " when three, one is opposite the " Dorsalfach," and the two 

 others opposite the lateral " Ventralfach." In Alveolites the one tooth is ventral instead 

 of dorsal. 



Alliance of Syringopora with Tubipora. — In Syringopora the septa seem to be very 

 much of the same nature as in Heliopora ; and in Heliopora, as already described, the 

 tabulae are not merely transverse floors, but the bottoms of cups of hard tissue fitted 

 inside the older tubes and calicles. In Syringopora this condition of the tabulae is much 



