THE MEDUSiE OF MILLEPOEA MURRAYI. 215 



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. 



Fia. 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-nucleatejd endoderm, which is continuous with 

 the endoderm of the trophodisc. 



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

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

 from the very first quite distinct from one another. 



Fig. IS.^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 ampuUse. 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 AUopora, 

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

 and End.) surrounding the spermarium. 



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

 stock 6i 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 ampullae are occupied by planulse. Below the ampullse there may be 

 seen in the endoderm of the canals some very young eggs, containing no- 

 yolk-granules and showing blimt amoeboid processes. 



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

 section. The germinal vesicle (Oerm. Yes) 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 xa^ in Fig. 23, showing the 

 twelve pouches of its margin. 



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

 planula, and below it a young ovum in a young trophodisc. 



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