212 SYDNEY J. HICKSON. 



Fig. 6. — An aggregation of spermospheres {Sperm. S-^.) at the peripheral 

 extremity of a dactylozooid, sunk in a cup-shaped receptacle. At Umh. may 

 be seen the first trace of the 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 {Naniat.). 



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

 pletely developed, but the endoderm is much thinner than it is in Fig. 8. 

 The spermarium is much larger, but there is no trace of a manubrium. 

 The dactylopore is completely closed by an operculum {op.) formed by 

 flattened strap-shaped ectoderm cells. 



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

 manubrium {man.), containing a cavity continvious 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 gonangiiim. 

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

 ready to escape. The umbrella {Umh.) 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 XIV. 



Fig. 12. — Transverse section through a decalcified branch of Disti- 

 chopora, showing the male gonophores lying in the ampullae. One, two, 

 or three gonophores occur in each ampulla. At the edges of the branch 

 are situated the rows of dactylozooids {Dact. Z.) and gastrozooids {Oast. 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 



