Panorama (4 images) of tissue section across top of medusoid

 First: here's a phase contrast image of a medusoid, zoomed out, surrounded by tissue of the ampulla.  Notice the proximity to the surface.  The dip at the top is due to degrading tissue, accompanying decalcification of the cover of the ampulla.

 

 

A drawing from Hyman, The Invertebrates, Vol. 1. of a medusoid within the ampulla, in situ.   The other images here are from earlier in the cycle.  There is evidence of decalcification.  

The life cycle of Millepora spp. is a multipart symphony.  The developmental sequences of Zooxanthellae, the skeleton, the gametes, and the medusoid all must  proceed as one.  A large number of Zooxanthellae, below, are dividing, as they accumulate near the dense part of the ovum.  

Ex Hyman:  Medusoid within ampulla with ova.

 

 

 

 Now a panorama across a similar cross section on the same slide. 

 

 This image shows the tissue across the region of the top of the ampulla that had been decalcifying, prior to liberation of the medusoid.  

 

The following section was cut across what I think is the Velar Plate, which will open up to leave a velum around the periphery of the medusoid, allowing propulsion to occur.

 

Medusoid of Millepora sp.  The velum (v) projects inward from the umbrella margin.