182 SYDNEY J. HICKSON. 



these medusee exactly fit into the ampullar cavities of the 

 skeleton, and form the only explanation of their presence. 

 The eggs of this species are, as in Millepora plicata (6), 

 very small and contain no yolk, and I have seen no embryos 

 and no parasites that could cause or fit into these cavities. 

 Quelch's ampuUse, then, are the cavities that contain male 

 medusae. 



The Structure of the Medusae. — The medusae may be 

 found in all stages of development in the different parts of the 

 same branch. They are very irregularly distributed, and it is 

 difficult at present for me to give any hints to guide natural- 

 ists in the search for them. They are never found, so far as 

 my experience goes, close to the free extremities of the 

 branches. In my specimens they were found in greatest 

 abundance at a distance of three-quarters of an inch to one 

 inch from the free extremity, but a few specimens were found 

 quite close to the attached base of the colony. Some branches 

 appear to be devoid of them. 



All the stages of development may be found with care and 

 patience, but the stage represented in fig. 10 is the most fre- 

 quent in my preparations. 



A central manubrium {Man.) hangs in the sub-umbrella 

 cavity bearing the large spermarium (Sperm.). It is composed 

 of irregular endodermal cells, and contains a considerable cavity 

 continuous with the cavity of the subjacent coenosarcal canals. 



The SPERMARIUM appears to be double in section, but is 

 really saucer-shaped. It contains a large number of spherical 

 spermoblasts lying in a homogeneous fluid (?). It is covered by 

 a very thin coat of flattened ectoderm cells continuous with the 

 inner ectodermic lining of the umbrella. 



The UMBRELLA is composed of three layers : a median layer 

 of solid endoderm continuous with the endoderm of the manu- 

 brium, and an inner and outer sheath of ectoderm continuous 

 with one another at the free rim of the umbrella. 



The inner sheath of ectoderm is, as mentioned above, con- 

 tinuous at its proximal side with the thin coat of ectoderm 

 covering the spermarium. The outer sheath is continuous 



