246 J. H. ASHWORTH. 



Introduction. 



At the suggestion of Professor Hickson I undertook to 

 examine a specimen of the Alcyonaceous coral Xenia, which 

 he had collected on the reefs of Talisse Island, North Celebes, 

 chiefly with the intention of working out the arrangement of the 

 canals of the colony. As the investigation proceeded the pre- 

 servation of the colony was found to be so exceptionally perfect 

 that it seemed desirable to make a study of its histology, and as 

 several new and interesting points were early observed I finally 

 decided to work out iu detail the complete anatomy and histo- 

 logy of the colony. Although many authors have described 

 the external characters of various species of Xenia, few have 

 paid any attention to their internal structure. Bourne (1895) 

 has referred to the canal system, the mesogloea, and the 

 distribution of spicules in two species of Xenia, and in 

 Heteroxenia Elizabethse, and Kolliker (1874) described 

 the anatomy of his new Heteroxenia Elizabethse as far as 

 its very imperfect preservation would permit. These two 

 accounts contain practically the whole of our knowledge of 

 the internal structure of these two genera, and hence, when 

 the beautiful preservation of this colony of Xenia from Talisse 

 was apparent, there was a strong inducement to attempt a more 

 complete account of its detailed anatomy and histology. 



The work has been carried on during the past two years in 

 the zoological laboratories of the Owens College. My best 

 thanks are due to Professor Hickson for the beautifully pre- 

 served specimen upon which most of my work has been done, 

 and for advice and criticism given during the progress of the 

 work. I am li.so indebted to Professor Lankester for a speci- 

 men of Heteroxenia Elizab ethse, to Mr. J. S. Gardiner for 

 a specimen of Xenia from Rotuma, and to Dr. Arthur Willey 

 for fourteen specimens of Xenia from various reefs in the 

 Pacific. 



External Characters of the Colony (PI. 23). 

 The Xeniidae are distinguished from all other Alcyonaria 

 by their soft, fleshy consistency and non-retractile polyps. The 



