THE STRUCTURE OF XENIA HIOKSONI. 



287 



Measurements of the Autozooids of Heteroxeuii 

 Elizabethae. 



External Characters of the Siphonozooids of 

 Heteroxenia Elizabethse. — The siphonozooids^ like the 

 autozooids^ are non-retractile. Tliese vary in lengtli from 

 1*8 ram. to 5*0 mm., and are "5 mm. to 10 mm. wide. Their 

 tentacles are all in the same condition, and are mere lobes 

 from "2 mm. to "25 ram. in length, and never show any traces 

 of the formation of pinnules. It will be seen from the 

 appended table that there is no developraent of the tentacles 

 corresponding to the increase in length of the individuals, so 

 that the tentacles of a zooid 5 mra. in lengtli are very 

 sirailar to those of a specimen less than half its size (compare 

 S 1 and S 7 in table). 



