82 INVERTEBRATE ANIMALS. 
carbonate of lime. These are probably rudimentary organs of 
hearing. Others of the marginal bodies are in the form of little 
masses of colouring-matter or pigment, often of a strikingly 
bright colour, enclosed in distinct cavities. These are known 
as the “ pigment-spots” or “eye-specks,” and they are believed 
to be rudimentary organs of vision. They are placed in a con- 
spicuous and unprotected position on the margin of the disc, 
and hence these organisms were termed “naked-eyed” Meduse 
by Edward Forbes. The reproductive organs are mostly de- 
veloped in the course of the radiating gastro-vascular canals, 
‘but are sometimes situated in the walls of the central polypite. 
The above is the essential structure of any of the ordinary 
naked-eyed Meduse; and it is hardly necessary to remark that 
it is exactly similar to what has been formerly described as 
distinguishing the undoubted free-swimming reproductive buds 
of the fixed Hydrozoa. The probabilities, therefore, as before 
said, are in favour of the belief that the entire group of the 
Discophora will have to be ultimately done away with. 
The naked-eyed A/eduse (fig. 26), are all exceedingly elegant 
and attractive, when examined in a living condition, resembling 
little bells of the most transparent glass, adorned here and there 
with the most brilliant colours. They occur, in their proper 
localities and at proper seasons, in enormous numbers, and 
they constitute one of the staple articles of diet to the Green- 
land whale. They are mostly phosphorescent, or capable 
of giving out light at night, and they appear to be one of the 
principal sources of the luminosity of the sea. It does not 
seem, however, that they phosphoresce unless disturbed or 
irritated in some way. 
