THE MEDUSA OF MILLEPORA MUERAYI. 407 



cells, the undeveloped seminal duct. The trophodisc {troph.) is reduced to an 

 irregular mass of endoderm cells. 



Fig. 15. — Section through a very young male gonophore of Distichopora. 

 The young spermarium (sperm.) lies apparently between the ectoderm and 

 endoderm of the bud, but the endoderm is cup-shaped, and the margins of the 

 cup project between the ectoderm and the proximal hemisphere of the 

 spermarium. 



Fig. 16. — Section through an older male gonophore of Distichopora, 

 showing the spermarium covered by the two membranes, a thin nucleated 

 ectoderm and a thinner non-nucleated endoderm, which is continuous with 

 the endoderm of the trophodisc. 



Fig. 17. — Section through the earliest stage I have found of the formation 

 of the seminal duct. The ectodermic and endodermic elements are from the 

 very first quite distinct from one another. 



Fig. 18. — Section through a seminal duct of a ripe male gonophore, open 

 to the exterior. 



Fig. 19. — Section through a portion of a decalcified branch of Allopora, 

 showing three male gonophores lying in their ampullae. As a rule, only one 

 gonophore is found in each ampulla ; but one case is figured (gonophore 2) in 

 which a large gonophore and a very young bud occur in the same ampulla. 



Fig. 20. — Section through a nearly ripe male gonophore of Allopora, 

 showing the club-shaped endodermal spadix, and the two membranes {Ed. and 

 End.) surrounding the spermarium. 



Fig. 21. — Section through a portion of a decalcified branch of a female 

 stock ol Distichopora, showing a number of ova and planulse in various 

 stages of development lying in their ampullae. 



Fig. 22.— a portion of the same as Fig. 21, more highly magnified. The 

 ampulla; are occupied by planulse. Below the ampullae there may be seen in 

 the endoderm of the canals some very young eggs, containing no yolk-granules 

 and showing blunt amoeboid processes. 



Fig. 23. — An ovum of Distichopora that is nearly mature, as seen in 

 section. The germinal vesicle {Germ. Fes.) lies near the superficial side of 

 the egg, and is surrounded by small yolk-granules. The trophodisc is simple, 

 in vertical section, and contains a pronounced lumen. 



Fig. 24. — Transverse section through an ovum and trophodisc of Disti- 

 chopora in the plane represented by the line .r .r' in Fig. 23, showing the 

 twelve pouches of its margin. 



Fig. 25. — Section througli an ampulla of Distichopora, containing a planula, 

 and below it a young ovum in a young trophodisc. 



VOL. XXXII, PART III. — NEW SEE. D D 



