No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 211 
When the various elements of the ectoderm have been com- 
pletely differentiated, Fig. 26 (from a stage a trifle older than 
Fig. 29), a finely striated cuticle is secreted, in all respects like 
that described by the Hertwigs for the actinias (g. Taf. III.). 
The cilia with which the body ectoderm is completely covered, 
and with which the cesophagus and filaments are likewise pro- 
vided, I have not represented in the figures. 
b. Esophagus and Filaments. 
The cesophagus and young filaments, Fig. 20, have the same 
structure as the superficial ectoderm, except that mucus cells 
are absent, and the granular gland cells more abundant than 
over the general surface. Asarule it is only in the youngest 
stages that the reflected ectoderm, Fig. 18, contains gland cells, 
and even then they are rare. In later stages, Fig. 24, mucus 
cells are found in the upper part of the cesophagus immediately 
round the mouth, and very large thread cells, Figs. 24 and 27, 
appear in considerable numbers in the cesophageal epithelium, 
extending down into the filaments. The histology of the fila- 
ments will be treated in detail in a special section. 
c. Endoderm. 
The endoderm, after it has once formed, remains about the 
same during larval life. I am not sure whether it is ciliated. 
The cells are cubical or columnar, and contain one or more large 
and distinct vacuoles. The protoplasm is granular and coarsely 
reticular. The cell outlines can only be distinguished with a 
little care. The number of yellow cells steadily increases with 
age. A few very fine muscle fibres can be made out here and 
there, especially in the mesenteries, and a continuous layer 
probably exists. 
In closing, the general similarity between the ectoderm of 
the coral larva (practically the same in the adult Manicina) and 
the actinian ectoderm, as described by the Hertwigs, may be 
noticed. In particular, the two kinds of gland cells in the ac- 
tinias are exactly represented in the coral. The Hertwigs sug- 
gested that possibly the granular gland cell was but a stage in 
the development of the mucus cell; but this appears not to be 
the case, as the two are distinguishable from the start, and have 
also a different distribution. 
