638 EDWARD T. BUOWNE. 



and between these cells there are a few nematocysts, like 

 those found in the tentacles. 



Absence of sense organs. — When I saw the original 

 drawing of Plate 36, fig. 14, before I received the specimen, 

 1 thone-ht that the little circles at the bases of the tentacles 

 represented marginal sensory vesicles situated just above the 

 root of the tentacle. They certainly have the appearance of 

 sense organs with a single otolith. In diagrams, and often 

 in good drawings, sense organs are drawn in a similar manner. 

 I thoroughly searched the margin of the umbrella for sense 

 organs, finally using an oil immersion lens, but failed to find 

 any indications of a sense organ either at the base of the 

 tentacles or in between the tentacles. The margin of the 

 umbrella has a slight brownish colour, as if the Medusa had 

 been killed with Flemming's solution. All the nuclei are of 

 a faint brownish colour, easily seen with an oil immersion 

 lens, and the cell walls are also well defined, so that if any 

 sense organs had been present they ought to have been 

 visible. The little circles in the figure are intended for 

 optical sections of the bases of the tentacles. They represent 

 the attachment of the tentacle to the margin of the umbrella, 

 and have nothing whatever to do with sense organs. 



A Comparison between Limnocodium and Microhydra. 



When I first saw the drawings of Microhydra and com- 

 pared them Avith the figures of Limnocodium, it seemed 

 quite possible that Microhydra might turn out to be the 

 well-known Limnocodium, but after examining the Medusa 

 of Microhydra the idea of such a possibility soon vanished. 



Hydroid. — In the Hydroid phase the resemblance between 

 Limnocodium and Microhydra is very close, as will be 

 seen on comparing PI. 35, fig. 10, with PI. 36, fig. 17. In both 

 forms the hydranth has degenerated to its simplest condition — 

 i.e. to merely a body without tentacles, and when the native 

 place of Limnocodium has been discovered we may obtain 

 a clue to the cause of degeneration. 



