A iichori ii;j Tubes of Adeona. 3 



An examination of incinerated fragments and of a number of 

 sections of the anchoring tubes of a dried, recent specimen shows 

 that their structure is identical with that just described in the 

 fossil. Each branch of the " root," in short, is a bundle of 

 tubes arranged in several concentric circles. In the calcareous 

 segments these tubes communicate with one another by fine 

 connecting tubules, which do not apparently occur in the chiti- 

 nous segments, where the tubes remain distinct and separate 

 from one another. 



The chitinous tubes are continued as a lining for a variable 

 distance into the canals of the calcarous segments, and occasion- 

 ally chitin may be traced into the connecting tubules. Judging 

 by Kirchenpauer's description and figure he appears to have not 

 noticed the larger canals in the calcareous segments, but to have 

 seen the smaller ones only.* The structure of the rooting organ 

 would be then, as he remarks, entirely different from that of any 

 other genus of Cheilostomata, as in all other instances it consists 

 of a chitinous tube more or less encrusted with calcareous matter. 

 It will, however, be seen that the differences are not as great as 

 lie thought, though the alternation of calcareous and chitinous 

 joints still marks it off strongly from the attaching structure of 

 all other polyzoa. 



Nicholson f figures the central portion of a transverse section of 

 the zoarium of a recent Cellepora which shows practically the 

 same structure as is seen in the rooting " organ " of Adeona. 

 Sections which I have made of Cellepora incrassata from the 

 Kara sea show that towards the centre of the older portion of a 

 branch the zocecia have assumed an elongate tube-like form, and 

 the communication tubes have the appearance described by 

 Nicholson. In the younger parts of a branch, that is towards its 

 distal end, the structure is very like that shown in Nicholson's 

 tig. 152, C. The modifications of the skeleton have their parallel 

 in those of the zooids which build up its different parts, and the 

 polymorphic character of the polyzoon colony has long been 

 recognised. 



The genus Adeona is restricted to the southern seas, several 

 species having been recorded from Australia and South Africa. 



* (Jeber die Biyozoen-Gattung Adeona. 



t Manual of Paleontology, Nicholson and Lydekker, 3rd ed., vol. i., p. 687. 



1a 



