THE STRUCTURE OF XENIA HIOKSONI. 297 



25, fig. 8. Its tentacles bear near the tip one pinnule on each 

 side of the axis. The stomodseum is -74 mm. long, and exhibits 

 a well-marked siphonoglyph, bearing flagella in its lower half. 

 The dorsal mesenterial filaments are well developed, and extend 

 in a sinuous course nearly 1 mm. down the coeleuterou. The 

 coeleuteron extends 1-4 mm. into the stem, curving so as to be 

 parallel to the neighbouring coelentera. Its connections with 

 the longitudinal and superficial canals may be seen in the 

 figure. The flagella of the endoderm cells attain 40 fx in length. 

 The distribution of spicules, nematocysts, and zooxanthellse is 

 shown in the figure. In such a polyp all the adult structures 

 are differentiated. In the growth of the polyp, from this 

 point onwards to the full adult size, there are few features 

 which call for comment. The chief of these are the formation 

 of a greater number of pinnules on the tentacles ; the elonga- 

 tion of the ccelenteron outwards (as the free portion of the 

 polyp grows in length) and inwards into the mesogloea, where 

 it curves, so as to lie parallel to the neighbouring coelentera 

 (PI. 25, fig. 8) ; the increase in number and size of the giant 

 flagella on the endoderm cells, and the development of sperm 

 sacs on the mesenteries. 



General Summary. 



The following is a recapitulation of the new points to which 

 reference is made (paragraphs 1, 2, and 6 have been already 

 published in ' Proc. Roy. Soc.,' 1898) : 



1. The absence of ventral and lateral mesenterial filaments 

 usually present in the polyps of the Alcyonaria. The only 

 previously recorded examples of the absence of these filaments 

 are the siphonozooids which occur in some other Alcyonacea 

 and in Pennatulids. 



2. The absence of these filaments is correlated with the 

 presence of gland cells in the stomodseum, which occur espe- 

 cially in the ventro-lateral walls which abut on the siphono- 

 glyph. Their position is suggestive of the digestive function 

 of the cells, as their secretion can be readily poured out on 

 to the ingoing food particles. 



