596 SYDNEY J. HICKSON. 
over two years to bring to the state in which I am able to 
publish it. The first few preparations were made in the Mor- 
phological Laboratory at Cambridge, the research was continued 
during 1888 in the anatomical department of the University 
Museum at Oxford, and completed in the Laboratory of Compa- 
rative Anatomy at University College, London. I cannot close 
this paper without expressing my sincere thanks to Professor 
Lankester for allowing me the use of a table in his laboratory, 
and for the many valuable suggestions he has made to me 
during the course of my investigations. 
BIBLIOGRAPHY. 
1. H. N. MosrLtey.—* Report on Certain Hydroid, Alcyonarian and Madre- 
porarian Corals procured during the Voyage of H.M.S. ‘Challenger ’ 
in the years 1873-76,” ‘‘‘ Challenger ” Reports,’ vol. iii. 
2. S. J. Hickson.—“ On the Sexual Cells and Early Stages in the Develop- 
ment of Millepora plicata,” ‘ Philosophical Transactions,’ 1888. 
DESCRIPTION OF PLATE XXXVIII, 
Illustrating Dr. Hickson’s memoir ‘On the Maturation of 
the Ovum and the Early Stages in the Development of 
Allopora.” 
The following Reference Figures are used throughout. 
ect. General ectoderm of the parent colony. ect’. Embryonic ectoderm. 
end. Kudoderm. m. Mesoglea. ov., ov*., ov®, Ova. tv. Trophodise. 
ch. Chorion. g.v. Germinal vesicle. g.s. Germinal spot. 2. Nucleus. 
y. Yolk-globules. /. Lumen of canal. p. 4. Polar bodies. 
Fig. 1.—A small portion of the canal system of Allopora. In the larger 
canals, @ and 4, a lumen may be seen ; but in the smaller ones, ¢ d, this is not 
apparent. The endoderm is traversed by a coarse protoplasmic spongework, 
with nodal thickenings. There are no traces of any boundary membranes 
between endoderm cells. The ectoderm is like the endoderm in general 
structure, but it is distinctly divided into separate cells each containing a 
single (frequently flattened) nucleus. Between the endoderm and ectoderm 
there is a thin layer of mesogloea. 
