4 ARTHUR DENDY. 



Whether the medusoids naturally separate from the 

 hydroid I cannot say from direct observation. They ex- 

 hibited slight twitching movements of contraction, however, 

 while still attached to the parent, and the structure of the 

 larger ones leaves no doubt that they ultimately become free- 

 sAvimming. Moreover many of them became detached when 

 the organisiQ was killed. 



3. The Hydroid. 



(a) External Characters. — The body of the hydroid is, 

 as compared with the ordinary hydroid type — such as we see, 

 for example, in Tubularia, — greatly modified in form and 

 structure, and the modification is such as to bring about the 

 necessary adaptation to the changed conditions of life. The 

 usual stalk is entirely wanting, nor is there the slightest 

 indication of its having ever existed. The aboral portion of 

 the body is enormously swollen out, and quite evenly rounded 

 off at the upper pole, forming the nearly spherical "float." 

 To the lower pole of the float is attached the cylindrical " pro- 

 boscis," bearing the mouth at its extremity. The line of 

 junction between the float and the proboscis is well marked 

 even externally, and corresponds to an even more pronounced 

 internal demarcation between the two. 



The float carries numerous long tentacles, which are 

 scattered without any definite arrangement at approximately 

 equal distances from one another all over its surface. These 

 tentacles are cylindrical and bluutly rounded at the extremity, 

 never distinctly knobbed. When fully extended they may be 

 about as long as the float itself. For the most part they are, 

 as usual amongst the Hydrozoa, unbranched, but two or three 

 were observed each with a single branch (figs. 3, 5, B.T.), 

 this condition being probably abnormal. 



The proboscis is differentiated transversely into two por- 

 tions (fig. 2). The upper part bears no tentacles, and 

 exhibits an appearance of circular and longitudinal striation, 



