MATURATION OF OVUM OF ALCYONIUM DIGITATIUM. 497 
appears to be of exactly the same specific gravity as the sea 
water, floating at any depth, but I found that unless an 
egg is fertilised it sinks to the bottom of the tank after some 
hours. 
The nucleus of the immature ovum is a large, oval, eccen- 
trically placed structure, resembling that described in many 
cceelenterates. The chromatin is aggregated into a single 
spherical vacuolated ‘‘nucleolus”’? (Fig. 1). The achromatic 
nGie 
Fic. 1.—Section of a maturing ovum taken from. polyp. x 120 diams. 
Fre. 1 a.—Nucleus of same drawn with Zeiss oil. imm. apoch. 
network is scanty and wide-meshed, and is very sensitive to 
the action of acetic acid. With too strong a solution of 
corrosive acetic it almost entirely vanishes, leaving the mass 
of chromatin lying in a hollow vesicle. 
The changes that now take place are quite unlike any 
that have hitherto been figured or described. Instead of 
the nuclear membrane dissolving and two mitoses taking 
place without an intermediary resting stage, nothing of the 
kind happens. Of this fact I feel convinced. Of the large 
number of eggs examined I have never seen the smallest 
voL. 49, PART 3,—NEW SERIES. 36 
