I20 Natural History Bulletin. 



In the study of this species I have been profoundly im- 

 pressed with the completeness of the mechanism by which 

 every living part is constantly bathed in a current of water 

 bearing the various materials utilized by the polyp and other 

 parts of the zoanthodeme in the various life processes. When 

 we consider the large amount of lime, for instance, which 

 must be collected from the water to form the great mass of 

 spicules with which the zoanthodeme is fairly packed, the 

 necessity for this wonderful water-vascular system is evident. 



Axis cylinder. This structure, so characteristic of the 

 GoRGONiDiE, presents some features of peculiar interest in this 

 species. It may be described as the organ of support of the 

 zoanthodeme and its several branches. It is an axial frame- 

 work which sustains the whole fabric and expanding at the 

 base, forms the principal surface of attachment to the rocks 

 or bottom. Bs'' its flexibility it permits considerable move- 

 ment of the branches, and an}' one who has seen these zoan- 

 thodemes gracefull}- waving in the undulations of the water, 

 will at once be struck by the applicability of the old name 

 Zoophyte. The resemblance of the naked axis cylinder with 

 its spreading base and gracefully curving branches and woody 

 appearance, extending even, as it does in this species, to a 

 simulation of ^\\^ grain of zvood, is so striking, even startling, 

 that little blame is to be attached to those early naturalists 

 who claimed that the polyps of these Zoophytes had simpl}-- 

 spread over and encrusted the dead branches of some plant. 



The axis cyHnder of P. dichotoma is composed of two dis- 

 tinct parts (PI. II, fig. 7), an inner horny core or medullary 

 portion (b) and an outer semi-calcareous cylinder (a). The 

 former is simply a solid core of homogeneous matter which 

 appears much like the basal substance of the coenenchyma. 

 It is somewhat translucent and appears, when examined under 

 the microscope, to be built up, as it were, of superinsposed 

 lamellag which are quite thin and present markings like 

 wrinkles on their surfaces. To use a somewhat homely 

 simile, the central part of the axis cylinder looks like a pile 

 of very thin gun- wads or a rouleau. 



