190 ON THE PELAGIC FAUNA OF PLYMOUTH FOR SEPTEMBEK, 1897. 



tive cells. The third stage was not seen this year. I have noticed in 

 other species of medusae that the gonads may become mature in a 

 medusa which has not reached its maximum growth. The generative 

 cells sometimes develop and ripen faster than the medusa grows, and 

 consequently the ova or spermatozoa are shed earlier. It is possible 

 that a medusa may sometimes begin to shed ova at an intermediate 

 stat'e of growth and continue to shed them at intervals, until it reaches 

 its maximum growth. All the ova are not usually ripe at one time. 



The early ripening of the generative cells has led to many medusae 

 being described as distinct species. It has given me considerable 

 trouble in tracing the life-history of a species, as it is difficult without 

 a large number of specimens to trace and connect the different stages. 



Margellium odopuoictatuni has often ripe gonads in the later stages, 

 and the specimens which show the maximum growth are scarce. I 

 have only taken them in Valencia Harbour. The maximum growth 

 of a medusa is apparently only reached under very favourable con- 

 ditions. Hylococlon jprolifer when fully grown has three tentacles, but 

 ripe generative cells are often present in forms with two tentacles. 

 Medusae belonging to the genus Phialidium show often the early 

 ripening of the generative cells in the intermediate stages, which has 

 led to the description of a large number of spurious species. I believe 

 that Saphenia mircibilis will ultimately be shown to be a stage in the 

 development of Eutima insignis, yet both forms are frequently taken 

 with ripe generative cells. In the present list of species both names 

 are given, as my observations require further proof. 



Gytceis sp. (?). — This medusa is not described in Haeckel's Monogra'ph. 

 I have only found it in Plymouth Sound — a few specimens in 

 1893 and many in 1897. A description of the medusa, with 

 figures, is now in preparation. 



Tiara pileata. — Only young stages seen. 



Euphysa aurata. — A single specimen taken. This species is new to 

 the fauna of Plymouth. 



Irene pellucida. — Only young stages seen. 



Mitrocomium sp. (?). — This medusa is not described in Haeckel's 

 Ilonograjyh. A description of the species is in preparation, as 

 enough specimens have now been collected to connect the dif- 

 ferent stages. I obtained few specimens in 1893 and 1895. 



Liriantha appendiculata. — All the specimens belonged to early stages. 



Sarsia gemmifcra. — A young stage with medusa-buds. 



Gemmaria implcxa. — An early stage. The hydroid form has not been 

 recorded for Plymouth. 



