346 L. MDRBAOH. 



endodenn, tlie ectoderm being quite clear. Both these layers 

 as well as the raesoglcea have the typical cojlenterate character, 

 aud will not need further notice. 



The hydranth does not terminate immediately below the 

 aboral tentacles, but, as is evident from its internal and its ex- 

 ternal character, it extends over one third its length farther 

 down to where it unites with the body. Just below the point 

 where the aboral tentacles are attached there is an enlargement 

 in the digestive cavity, looking like a deeply pigmented band 

 running across the coelenteron, for which I have so far found 

 no adequate explanation. Where the hydranth joins the 

 hydrocaulus there is a ring-like expansion, which gives the 

 appearance of the former being stuck on to or slipped over the 

 end of the latter, like a collar or flange (fig. l,c.). In an 

 expanded condition of the body it is nearly obliterated, becom- 

 ing more prominent again after contraction has returned the 

 body to its normal. It marks the upper limit of the perisarcal 

 tube, and this being a rather tightly fitting structure may in 

 part account for the changeable character of the collar. 



Large numbers of nettling organs are present in the lower 

 edge of the collar, aud although they are apparently complete 

 for use are nevertheless not destined to be used here, for there 

 are no cnidocils present. They migrate from the collar toward 

 the tentacles, and are of no service until they reach these and 

 become erect. Of the nettling organs in general it may be 

 here added that there are at least two kinds, similar in shape 

 but differing in size and structure. They are very short 

 ovals. 



The hydrocaulus is somewhat more slender than the adjacent 

 portion of the hydranth, and gradually narrows down to the 

 taper-pointed foot end, which is generally curved and forms a 

 better rest for the polyp (fig. l,h.c.). The character of its 

 layers is practically the same as that of the hydranth, added 

 only to this that the ectoderm cells differ physiologically in 

 that they secrete the perisarc-like tube. A portion of the 

 foot end is frequently of a deeper pink hue, indicating greater 

 activity here ; but as this has to do with reproduction it will 



