DISCOPHORA. 75 



naked-eyed Medusae, which can be shown to be of this nature, 

 cannot, of course, be regarded as distinct animals at all. Still, 

 there remains a considerable group of naked-eyed Medusce to 

 which this explanation has not hitherto been shown to apply. 

 In most of the members of this group the course of develop- 

 ment is quite unknown, and therefore their true nature is a 

 matter of doubt. Two families, however, of this group are 

 stated to produce eggs which develop directly into Medusce, 

 such as those which gave origin to the eggs ; and, if this ob- 

 servation is confirmed, these, at any rate, must be regarded 

 as true Discophora. In the mean while, therefore, it is best 

 to regard the group of the Discophora or Medusidce as of a 

 questionable nature, and as including forms which may ulti- 

 mately be shown to be nothing more than the detached zo5ids 

 of other Hydrozoa. Under these circumstances it will not be 

 requisite to do more than very briefly to describe the anatomical 

 structure of a typical Medusid / and this is the less necessary, 

 since it will be seen at once that the structure is in all essential 

 respects identical with what has been already described in 

 speaking of the free medusiform gonophores of the Hydroid 

 zoophytes. 



In all the naked-eyed Medusce, of which Modeeria (Fig. 21) 



FIG. 21. Naked-eyed Medusae, a Sarsia gemmifera; T> Modeeria fomnosa ; c Polyxe- 

 nia Alderi (after Gosse). 



