HYDROZOA. 129 



Hydrozoa may here be inserted. This property- 

 has been observed in most orders of the class, 

 though, among the Fhysophoindce, 8tephaii07nia, 

 and, of the LucernaTidcv, Pelagia are most re- 

 markable for its manifestation. Some, however, 

 of our more common jelly-fishes are also luminous. 

 It does not appear that, in any of these, special 

 light-giving organs exist. In the Medusidce, the 

 phosphorescence chiefly arises from around the 

 marginal bodies, but, in some instances, it is 

 emitted by the reproductive swellings, and, occa- 

 sionally, by the walls of the central polypite. 

 Our own Thaumantias lucifera, a species by no 

 means rare, displays this phenomenon in a very 

 beautiful manner. The little creature, when ir- 

 ritated b}'- contact of fresh-w^ater, marks its position 

 by a vivid circlet of tiny stars, each shining from 

 the base of a tentacle. 



Such small Medusidce are, doubtless, more 

 efficient in promoting the luminosity of the ocean 

 than their larger and, at times, more brilliantly 

 conspicuous congeners. But the fixed Hydrozoa, 

 which, obviously, can take no share in this display, 

 are, also, eminently phosphorescent. A remark- 

 able greenish light, like that of burning silver, 

 may be seen to glow from many of our native 

 Sertidaridce, becoming much brighter under 

 various modes of excitation. It is an error to 

 suppose, however, that thus alone do these cold, 

 oily, flames emanate. "If (writes Professor E. 

 Forbes) a bunch of one of the bushy corallines, 

 such as Sertularia abietina, be plunged when 

 active and alive imto fresh-water or spirits, a 

 gorgeous display of living stars is instantaneously 

 produced." 



