SYNCORYNE. 49 



and S. Sarsii no furrows have been observed. The gono- 

 zooids of these two species, and of the Stauridium pro- 

 ductum, seem to be perfectly similar in all external cha- 

 racters, at least in the first period of their free existence. 

 Observations are still wanting to show whether differences 

 arise in the further course of their development. 



The researches of Agassiz have proved that the free 

 zooid of S. gravata (C. mirabilis, Agass.) assumes, when 

 mature, the form of Sarsia, a genus founded by Lesson 

 for a " Naked-eyed Medusa," whose most striking charac- 

 teristic is thf remarkable length and extensibility of the 

 manubrium. It was discovered bv the distinguished 



v 



Norwegian naturalist whose name it bears. 



The changes which the zooid of S. gravata undergoes 

 in its progress towards maturity seem to be almost con- 

 fined to the manubrium. There is a slight alteration in 

 the shape of the umbrella, but no increase in the number 

 of tentacles with age. The manubrium in the adult 

 state, when extended, is twice or three times the length 

 of the umbrella. The upper portion, by which it is sus- 

 pended from the centre of the crystal dome, is thinner 

 than the rest ; the middle region is somewhat inflated (and 

 it is here that the ova are developed), whilst towards the 

 free extremity it is more or less clavate in form [Plate 

 III. fig. 3]. At the time of liberation, the manubrium 

 is of moderate dimensions, and does not extend to the 

 mouth of the bell. It is probable that in all the species 

 of Syncoryne the free zooid passes through a similar 

 change. 



We are also indebted to Agassiz for the interesting- 

 observation that the gonozooid in some cases presents a 

 very different appearance in the early and latter part of 

 the breeding-season. In the one it is free and perfectly 

 developed; in the other it is sometimes reduced to a fixed 



