196 Proceedings of the 



branous expansion, or breaks into a loose network of delicate 

 anastomosing tubes, which traverse every cranny and furrow of 

 the shell, and can only be detected after their tissues have been 

 coagulated by immersion in alcohol. On these, polyps are 

 developed at long intervals ; and in the larger tubes an inter- 

 mittent circulation of shining globules may be detected by 

 the aid of high microscopic power and direct sunlight. In 

 specimens which have been long kept in captivity I have seen 

 these fibres throw up thick white stolons or suckers, tipped 

 with crimson, some of which have attached themselves to 

 the sides of the tank, expanded themselves into independent 

 polyparies, and afterwards put forth clusters of polyps. The 

 small living specimen on the table, of which fig. 12 is a draw- 

 ing, has been propagated in this way, and shows the tubular 

 structure of the polypary in an admirable manner. 



10. The life of the polypary is not dependent on the pre- 

 sence of the polyps. Many specimens of Hydractinia occur 

 in the winter, in which the polypary exists in a high state of 

 development, although its polyps are very few in number, or 

 altogether absent, and which nevertheless become clothed 

 with these organs on the return of spring. 



11. The minute anatomical structure of the polypary, the 

 nature of its connection with the corallum, and the mode of 

 secretion of the latter, cannot readily be investigated in those 

 specimens of Hydractinia which are parasitic on the shell of 

 the Pagurus, as the zoophyte is broken up by an attempt to 

 remove it from its site. A better opportunity for observation 

 is afforded when the animal has extended itself along a trans- 

 parent surface. The propagative stolon of Hydractinia, after 

 leaving the point of its origin, increases rapidly in diameter, 

 and throws out irregular branches, not unlike a very minute 

 specimen of Tubularia larynx. The tips of these branches 

 are covered with a glutinous cement, by which they attach 

 themselves tenaciously to glass or other surface near them. 

 Having attached themselves, they expand laterally, at the 

 same time throwing out finger-like prolongations, which, as 

 they come in contact with each other, coalesce, until a fleshy 

 plate is formed adherent to the glass. Polyps are deve- 

 loped both from the loose branches and the attached poly- 



