THE STRUCTURE OF XEXIA HICKS0XI. 



215 



two-fifths of the whole length of the polyp. With the increase in 

 length of the tentacles there is a corresponding increase in the number 

 of pinnules which the tentacles bear, and, as the following table shows, 

 there is a perfect series of examples, beginning with the very young 

 specimens, in which the tentacles are devoid of pinnules, and ending 

 with the largest polyps, whose tentacles show from the outer aspect 

 nineteen or twenty pinnules on each side of the middle line. The 

 gradual transition from the youngest to the oldest polyps shows that 

 the small individuals in this colony are undoubtedly young buds in 

 various stages of development. They are all " polyps," using the word 

 in the sense in which it was used by Kolliker. 





Total length 



Width 





Xumber of 





Reference 



of Polyp 



of 



Polyp. 



Length of 



Pinnules on each 





X umber. 



(Body and 



Tentacles. 



side of Tentacle 







Tentacles). 





(outer aspect). 







mm. 



mm. 



mm. 







I. 



•32 



•44 



•10 





PI. XIX., Figs. 4, 4A. 



II. 



•43 



•4 



•12 







Insect., PI. XXII., Fig. 28. 



III. 



•56 



•37 



•19 







— 



IV. 



•8 



•4 



•31 



trace of first 



— 



V. 



■95 



•35 



•34 



Trilobed = l 



PI. XIX , Fig. 5. 



VI. 



10 



•34 



•43 



Trilobed = l 



In section, PI. XX., Fig. 8. 



VII. 



1-1 



•5 



•53 



2 



— 



VIII. 



1-42 



•87 



•6 



4 



PI. XIX., Figs. 6, 6a. 



IX. 



1-6 



■96 



"7 



4—5 



— 



X. 



2-0 



•86 



•86 



6 



— 



XI. 



21 



•8 



1-03 



7 



— 



XII. 



2-27 



•6 



13 



8 



PI. XIX., Figs. 7, 7a. 



XIII. 



2-8 



•86 



1-4 



8 



— 



XIV. 



3-2 



•9 



1-4 



8—9 



— 



XV 



4-0 



1-0 



1-8 



10 



— 



XVI. 



6-1 



•9 



2 4 



10—U 



— 



XVII. 



6 '5 



•9 



2-5 



11—12 



— 



xvn r. 



6-8 



1-1 



2-85 



13 



— 



XIX. 



9-1 



1-2 



4 2 



14—15 



— 



XX. 



120 



1-2 



5-1 



17 



— 



XXI. 



11-65 



1-2 



57 



19-20 



PI. XIX, Fig. 2. 



I find in all the sixteen other specimens of Xenia at my disposal, 

 young buds in all stages of growth, similar to those described and 

 figured in Xenia Ricksoni. Most of these young buds occur on the 

 arched end of the stem, but in two of the colonies examined a few buds 

 are found in the middle portion of the summit between the bases of the 

 larger polyps. These buds, however, differ in no way from those 

 round the edge of the summit. 



