582 SYDNEY J. HICKSON. 
11. The primitive ectoderm spreads over the periphery until 
it entirely encloses the central protoplasm and yolk-mass. The 
last point to be enclosed is that immediately in contact with 
the trophodise (Pl. XXXVIII, fig. 17). The central mass of 
the young embryo at this stage consists of a highly vacuolated 
protoplasm containing numerous scattered nuclei and yolk 
bodies. 
12. The embryonic ectoderm cells are formed by the split- 
ting up of the protoplasm into columnar epithelial cells, each 
containing a single nucleus (Pl. XX XVIII, fig. 21). 
13. When the embryo possesses a complete columnar ecto- 
derm it is ready to escape. 
14. The mode of escape has not yet been observed, but 
there can be little doubt that it squeezes its way out through 
a channel that is prepared for it by the absorption of a part 
of the superjacent calcareous skeleton (Pl. XX XVIII, fig. 4). 
II. The Formation and Fate of the Trophodise. 
The female gonophores of Allopora have not been previously 
described, but cup-shaped structures bearing ova are figured 
and described by Moseley (1) in Errina labiata and Plio- 
bothrus symmetricus. In Errina “ the spadix is at first 
cup-shaped, the walls of the cup being composed of a very 
thick layer of endoderm. The cavity of the cup is directed 
towards the surface of the coral and within it rests the single 
large ovum with its distinct germinal vesicle and spot.” In 
Pliobothrus “ each ovum is developed within the cup of a cup- 
shaped spadix.” 
From this it is evident that a structure comparable to the 
trophodise of Allopora also occurs in other Hydrocorallines ; 
but the term spadix must be abandoned, for there is sufficient 
evidence to show that this structure is not homologous with 
the spadix of sessile Meduse. The “ trophodisc ” suggested by 
Professor Lankester is a far better word to use as it expresses 
thefunction it performs without indicating any homological com- 
parison. Before describing the stages in the development of the 
trophodise of Allopora it is necessary to run through briefly 
