Anatomy of Gorgonid.^. 157 



is room for secondary canals: while minute spicules have little 

 room between them and the interspace can only be penetrated 

 by minute vessels, i. e., capillaries. This relation is true in 

 different parts of* the same zoanthodeme in which different 

 sizes of spicules are found. 



Axis cylinder. This is peculiar in having a relatively 

 small axial core (PL X, fig. 6, b), and a large apparently 

 structureless horny or chitinous investing cylinder. The 

 former presents the laminated structure which in many species 

 constitutes almost the entire axis cylinder, with which it is 

 probably homologous. The latter seems to be the homologue 

 of the structureless horny sheath which forms a thin invest- 

 ment of the axis in other species. It appears likely that the 

 axial core is produced by the growing tip as described on 

 page 132, and that the investing sheath is secreted by the 

 layer of endodermal cells immediately external to it. This 

 layer of cells is shown in fig. 5, c. The mesodermal cells are 

 columnar in shape and larger than those in a corresponding 

 position' in other species. 



The tip of the axis penetrates well within the body cavity 

 of the terminal calicle, hence reaches nearly to the surface at 

 the end of the branch. 



It is difficult to see how the frequent anastomoses between 

 different branches is accomplished. It may be that the axial 

 core, being very small, is produced with great rapidity and 

 forms the primary connection, and that the mass of the axis is 

 afterward produced by the endothelial investment in such 

 quantities as quickly to make a firm connection. 



ABSENCE OF NEMATOCYSTS IN GORGONIDiE. 



In none of the species described in the preceding pages have 

 I been able to find any nematocysts, or thread cells. A care- 

 ful scrutiny both of fresh and alcoholic specimens failed to 

 reveal a single one of these peculiar structures although the 

 writer was particularly anxious to find them if they existed. 



I That is surrounding the axis when it has attained its normal diameter, 

 not near the tip. 



