The Meduscn of Millepora. 



9 



and contains no nucleolus and very few or no chromatin granules. Its 

 outline is very ill-defined. The presence of zooxanthellse in the ovum 

 at this stage is of interest, and it is a matter for regret that I have 

 been unable to determine the manner in which they pass into the 

 cytoplasm from the endoderm of the medusa. 



In general characters the free ovum of Millepora has a remarkable 

 resemblance to the ova of Alcyonium and other Alcyonarians, and I 

 believe that this points to the conclusion that its specific gravity is 

 very slightly higher than that of sea water, and sinks extremely 

 slowly when set free. 



We are indebted to Mr. Duerden (1) for a brief account of these 

 medusge as observed in an aquarium (see figs. 4 — 9). " When first 

 liberated their walls appeared quite wrinkled, and the interior was 

 occupied with three or four opaque bodies (the ova). No stalked 

 tentacles were developed, their place being taken by four or sometimes 

 five swollen areas, where a few large stinging cells were located. 

 The medusae were very sluggish in their movements, feebly pulsa- 

 ting only now and again. While under observation a curious action 

 began to take place ; the opaque bodies in the interior were seen to 

 be extended through the mouth of the medusse " the mouth of 

 the umbrella cavity), "sometimes singly, sometimes two or more 

 partly connected. These became spherical, and appeared to have a 

 slight movement of their own. Having discharged themselves in this 

 way, the medusae shrunk up and their mission was apparently ended. 

 The whole process, liberation of the medusae and extrusion of the 

 spheroidal bodies, was completed in five or six hours." 



There are almost insuperable difficulties in the way of maintaining a 

 sea-water aquarium in the tropics in a thoroughly healthy condition. 

 I am satisfied that Mr. Duerden took every possible precaution, b#t 

 nevertheless it is probable that in some respects the conditions cannot 

 be relied upon as being strictly normal. The observations, however, 

 are of importance, the structure of medusa as it is seen in the ampulla 



Fig. 10. 



