406 SYDNEY J. HICKSON. 



extremity of a dactylozooid, sunk in a cup-sliaped receptacle. At Umb, may 

 be seen tlie first trace of tlie formation of the umbrella by the growth of the 

 endoderm. The position of the tentacles is still indicated by the rows of 

 small nematocysts. 



Fig. 7. — Section through another dactylozooid, showing a still further 

 growth of the folds forming the umbrella. All trace of the tentacles has 

 disappeared. 



Fig. 8. — Section through a young medusa of Millepora. The form of the 

 dactylozooid is completely lost. The endoderm of the umbrella is solid, and 

 much thicker than it is in later stages. The opening of the dactylopore can 

 still be traced, although it is blocked with the thickened ectoderm cells. The 

 pore is guarded by nematocysts {Nemat.), 



Fig. 9. — Section through another medusa. The umbrella is not completely 

 developed, but the endoderm is much thinner than it is in Fig. 8. The sper- 

 marium is much larger, but there is no trace of a manubrium. The dactylo- 

 pore is completely closed by an operculum {op.) formed by flattened strap- 

 shaped ectoderm cells. 



Fig. 10. — Section through another medusa, with a well-developed manu- 

 brium {man.), containing a cavity continuous with a large canal. The umbrella 

 walls are much thinner than they are in the specimens drawn in Figs. 8 and 9, 

 except at the margin. 



Fig. 11. — Section through a medusa that lies freely in the gonangiuni. It 

 is not connected organically with the colony at any point. It is probably 

 ready to escape. The umbrella {Umb.) is extremely thin, except at the 

 margins. There is a small cavity in the endoderm, but there is no mouth. 

 There are no tentacles, velum, nor sensory bodies on the margin of the 

 umbrella. Between the codonostome and the superficial ectoderm there is a 

 layer of mucus. 



PLATE XXX. 



Fig. 12. — Transverse section through a decalcified branch of Distichopora, 

 showing the male gonophores lying in the ampulla",. One, two, or three 

 gonophores occur in each ampulla. At the edges of the branch are situated 

 the rows of dactylozooids {Dad. Z.) and gastrozooids {Gast. Z.). 



Fig. 13. — Section through an ampulla of Distichopora, containing two 

 young male gonophores. Each of these is supported by its own trophodisc 

 containing a large lumen. 



Fig. 14. — Section through an ampulla of Distichopora, containing three 

 male gonophores in different stages of development. The largest of these 

 (1) contains ripe spermatozoa, and shows on its distal pole a conical cap of 



