Appendix to Hydractiuia. 



285 



endodermal tubes, and covered above and below by a deli- 

 cate investment of chitine. Found on the growing borders 

 of the zoophyte, and especially in cuttings of old specimens 

 transferred to glass. 



The spines are composed of one tube or many parallel 

 tubes: they may be single (PL XII. fig. 4), and developed 

 on a single tube of the polypidom, like those of Podocoryne 

 fucicola; single at their summits and of several tubes at 

 their base (figs. 5 and 6) ; composed entirely of several (8-12) 

 conjoined tubes (fig. 7) ; reticulate by the lateral anasto- 

 mosis of their tubes ; or consisting of long ridges of tubes 

 reared against each other. 



The polyps spring from one or several confluent tubes of 

 the polypary ; they are covered at their origin, and for a little 

 distance above it, by a delicate prolongation of the poly- 

 pidom. This may be detected by dyeing the whole zoophyte 

 with tincture of kino, which gives different tints to its 

 chitinous and fleshy elements, or by steeping it alternately 

 in spirit and water, when the coverings of the polyps and 

 polypary become inflated as in figs. 2 and 3. 



The polyps are of several shapes and functions, which I 

 have described in the paper cited above. It will be sufficient 

 to enumerate them here : — 



1. Alimentary polyps, with mouth and tentacles. 



2. Eeproductive polyps, with rudimentary mouth and 

 tentacles. 



3. Spiral polyps — a modification of the last; generally 

 barren (fig. 3). 



4. Sessile generative sacs of the polypary. 



5. Tentacular polyps, or great tentacles of the polypary 

 (fig- 2). 



In the reproductive organs of Hydractinia there is a 

 gradual transition from the reproductive polyp to the sessile 

 generative sac; the polyp loses its dot-like mouth, its ten- 

 tacles, its head or upper part, and finally dwindles down to 

 a mere sperm-sac. This change is generally seen in those 

 specimens which have long been kept in captivity. In these 

 specimens, too, many of the alimentary polyps are often 

 converted into large inflated sacs destitute of mouth and 



