286 J. H. ASHWORTH. 



Bourne provisionally referred this specimen to KoUiker's 

 species Heteroxenia Elizabethae, and, after comparing the 

 specimen with Kolliker's original account and figures (1874), 

 I can confirm his conclusion. This specimen is much smaller 

 than Kolliker's, its polyps being only about half the size, but 

 there are many points of agreement between them, viz. general 

 anatomy and proportion of parts, size, and structure of zooids; 

 size, colour, and distribution of spicules ; canals, &c. 



After carefully examining the two kinds of small individuals 

 (viz. young polyps and zooids), I have no doubt that tliey are 

 entirely different in nature. The external characters are quite 

 different, and there are important differences in their internal 

 arrangements, to which reference will be made. 



External Characters ofthe Young Polyps ofHetero- 

 xenia Elizabethae. — The youngest polyp, which is also by 

 far the smallest individual on the colonv, is '64 mm. in length 

 (fig. 38). Its tentacles are finger-shaped lobes "24 mm. to '3 

 mm. in length. The tip of one of the tentacles is slightly 

 three-lobed,but all the other tentacleshave simple rounded ends. 



A polyp 1*4 ram. long, the tentacles of which have attained 

 a length of "4 mm., are trilobed at their ends, i.e. the first 

 pinnule on each side of the axis is being formed. The 

 formation of pinnules proceeds regularly with the growth in 

 length of the tentacles, and the adult size and characters are 

 gradually attained. From the appended table it will be seen 

 that there is a complete series of stages from the smallest polyp, 

 •64 mm. long, with simple tentacles devoid of pinnules, to the 

 largest polyp, nearly 30 mm. long, the tentacles of which show 

 on the outer face twenty-four pinnules on each side of the 

 middle line. In this Heteroxenia the ratio between the length 

 of the tentacles and the total length of polyp is not quite as 

 constant as in the Xenia considered above. The tentacles 

 form about one fourth to one third the length of the whole 

 polyp. 



