ENTRY OF ZOOXANTHELLA INTO OVUM OF MILLEPORA. 697 
The Entry of Zooxanthelle into the Ovum of 
Millepora, and some Particulars concerning 
the Meduse. 
By 
Joseph Mangan, M.A., A.R.C.8e.1., 
Honorary Research Fellow of the University of Manchester. 
With Plate 18. 
During the present winter Prof. 5S. J. Hickson kindly gave 
me an opportunity of examining the material from Jamaica 
in which he discovered the female Medusze of Millepora 
(99). The results of my inqniry are mainly concerned with 
the manner in which the symbiotic zooxanthelle, found 
to exist in the free ova of that genus, infect the germ cells. 
I also wish to record the occurrence of free male medusz 
amonest the free female medusze collected in the above 
locality, and to make some remarks upon the oogenesis. 
THe INFECTION oF THE Ovum By ZOOXANTHELLA. 
In the earhest stages of the female medusa that came 
under observation the germ cells are arranged around 
the manubrium of the medusa, as a single layer, in most 
instances, in dome-shaped fashion. Each cell has well- 
defined boundaries, and possesses a large nucleus with in- 
tensely-staining chromatin nucleolus (fig. 1). The substance 
of the manubrium is vacuolated and scattered; in it lie 
numerous zooxanthelle, At the points where ova arise it 
would appear as if a gradual dissolution of the cell membrane 
took place between the cell destined to become the ovum and 
VOL. 93, PART 4.—NEW SERIES. AQ 
