FOSSIL CORALLINES. 41 



Mr. Hopkinson does not think there is any absolute 

 structural difference between Graptolites and Sertu- 

 larians, and his recent discovery of gonothecce (or egg- 

 bearing capsules) in Graptolites, similar to those seen 

 in Sertularians, has confirmed his opinion. 



In the " sea-firs " (Figs. 28 and 29), we have a horny 

 stem, hollow throughout, giving off branches, like a 

 miniature tree. These branches are also hollow, and 



Fig. 29. Common Sea-fir (Sertiilartct abietind). 



communicate with small cups called Hydrothecce. In 

 each of the latter a distinct zoophyte lives, capable of 

 slowly putting forth its fringe of tentacles beyond the 

 rim, and of withdrawing them again. Each individual 

 is connected, by means of the simple fleshy tissue 

 (caznosarc) which fills the hollow stems and branches, 

 with every other on the same colony or polypary. 

 At the base of each of the small cups is a partition, 



