VOL. LXVI.] PHILOSOPHICAL TRANSACTIONS. 725 



bands, whereof one part is of a rose colour, another yellowish, others white, 

 others more or less charged with colours, that form concentric circles like the 

 coats of an onion." This diversity of colours could hardly have taken place, 

 had there been a circulation of juices through the stem ; and it was probably 

 owing to the different food which the animals had lived on at different periods. 



There is another genus of zoophyte, which, though it swims freely about in 

 the sea, yet approaches near to the gorgonia, and will serve further to explain 

 the growth of its stem, and that is the pennatula, or sea-pen. This genus hAs 

 a bone along the middle of the inside, which is its chief support. This bone 

 receives the supply of its osseous matter by the same polype mouths, that 

 furnish it with nourishment. Dr. Bohadsch has very judiciously brought to this 

 genus the great Greenland clustered polype formerly described by me under that 

 • name, and now called pennatula arctica. In a cross section of the bone, (see 

 Philos. Trans., vol. 48), the several laminae are magnified, to show that they 

 are formed in layers like shells, and are not full of tubes as in a Vegetable 

 growth. These animals are ranged among the vegetating kind, and so called by 

 Dr. Pallas. There is a great affinity between the gorgonia and isis, so that the 

 increase of the bone of the latter will greatly illustrate that of the former. The 

 longitudinal section of the bone to the stem of the isis hippuris will show, that 

 it has been increased in diameter by successive layers of stony matter that 

 surround it; see fig. 7- In this instance we can trace the bone in its infant 

 state, when nature had given it pliable black horny joints, that it might yield 

 the better to the violence of the waves ; but as soon as it became stronger, 

 these horny bljfck joints were no longer necessary, as we find the lower part of 

 the stems totally overgrown with the bony substance. The furrows in this coral 

 are deeper than those of any other ; insomuch that not only the longitudinal 

 fleshy tubes that surround the bone, but even the minute pores in them, 

 through which the osseous juice exudes, are very discernible i see fig. 3. 



We now come to a very singular circumstance in the growth of the gorgonia, 

 in which it differs remarkably from thai of trees. Fig. 8, is the figure of the 

 naked stem or bone of a gorgonia, to which we find several tree oysters and 

 other shells have adhered. These shell fish seem to have killed the gorgonia ; 

 for the same stem seems to be covered over with another gorgonia of the same 

 kind ; which in its growth has almost covered the shells, and likewise the branches 

 to which they were fastened, leaving only part of the ends of the branches of the 

 first gorgonia yet uncovered. The size and weight of the shells probably gave 

 the waves so great a power over the stem, that it was at last broken off^ antf cast 

 on shore in the state in which it is here represented. This instance of a gor- 

 gonia growing over one of its own kind, seems sufficient to account for the 

 circle of calcareous matter found now and then in the cross sections of old stems. 



