8 



Mr. S. J. Hickson. 



absorbed into the substance of the large ova. The nucleus of the 

 oocyte seems to be disintegrated before complete fusion takes place, 

 since no degenerate nuclei can be found in the cytoplasm of the 

 large ova. 



The remarkably thick endoderm of the female medusa is a very 

 characteristic feature. It may be regarded as a special adaptation of 

 endodermal tissue for the purpose of affording nourishment to the 

 rapidly maturing ova, and similar in function to the trophodisc of the 

 Sty last erid^. 



At this stage several zooxanthellse (fig. 3, z) occur in the manubrium, 

 but none were observed in the cytoplasm of the ova. 



I have not been able to find evidence of the existence of an open 

 mouth in the medusae at this stage, but, bearing in mind the great 

 variability they exhibit, I cannot assert that a mouth never occurs. 



The margin of the umbrella exhibits three or four or five thickenings, 

 due to clusters of nematocysts (figs. 4 — 9), but no definite tentacles nor 

 sense organs were to be found after a most searching examination. 



Figs. 4—9. 



3. The liberated medusce. I have carefully examined the medusae 

 and free ova that Mr. Duerden collected in the water of his aquarium. 

 The medusae are so shrivelled and degenerate that nothing of their 

 anatomy could be satisfactorily determined. The ova, however, 

 appear to be in a satisfactory state of preservation, and exhibit one 

 or two features of interest. Each ovum of this series is approxi- 

 mately 0-25 mm. in diameter, that is to say, 0-05 mm. larger in 

 diameter than the ovum in the last stage. 



The cytoplasm is very granular and contains numerous vacuoles 

 and a few zooxanthellae (fig. 10, z). The germinal vesicle is very large 



