DEVELOPMENT OF CUCUMARIA ECHINATA 183 
owing to the high exteraal epithelium as stated above. It 
contains eges of various sizes. The egg is slightly flattened and 
is attached to the wall of the genital tube by its broad surface 
(Pl. 8, fig. 2), not by a slender stalk formed of the follicular 
epithelium, as described by Semper (47, 1867-8, p. 144), 
Jourdan (16, 1883, p. 52), and others in Holothuria.t 
The germinal vesicle (n) is large and spherical, lying eccentric- 
ally near the free end of the egg. The centre of the free surface 
is indicated by a minute conical process of the cytoplasm (ma). 
The gonad in the breeding season (PI. 8, fig. 8) has become 
thin-walled and yellowish in colour, containing still very small 
eggs as well as large ones, which latter are ready for spawning. 
The germinal vesicle (n) has now approached much nearer the 
free end than in the foregoing stage, leavmg a thin layer of 
yolky cytoplasm between it and the egg-membrane. Germinal 
spots (gs) are more minute and fewer compared with those in 
the early stage. 
The centre of the free surface is now very peculiar in structure. 
Here we see a compact cytoplasmic mass, of a somewhat fibrous 
nature, forming a short rod-like body protruding through the 
egg-membrane, with its free enlarged knob-like end attached 
to the follicular epithelium (Pl. 8, fig. 3, ma). Usually the 
proximal end reaches the germinal vesicle and becomes con- 
tinuous with its membrane, but in rare cases it ends apart 
from the germinal vesicle, where the latter is not very near to 
this pole of the egg. The space between the egg-membrane 
and the follicular epithelium (j) was perhaps occupied by 
a gelatinous layer. This remarkable structure, which I may call 
a micropyle appendage,” is only conspicuous in full-grown eggs, 
1 According to Hamann (15, 1884, p. 89) H. tubulosa is excep- 
tional ; here a fibrous bundle of connective tissue serves to fasten the egg. 
» As early as in 1851, J. Miller remarked that the ovarian egg of 
Pentacta doliolum is flat, and that at the centre of a flattened 
surface there is formed a yolky process which passes through the thick 
jelly layer investing the egg. He further observed a similar structure 
in some other Holothurians—T hyone fusus, Holothuria tubu- 
losa, &c. (‘Monatsber. Akad. Berlin’, April, 1851; ‘Phys. Abhandl. 
kon. Akad. Wiss. Berlin’, 1852 (1850), p. 77, Taf. LX, fig.8,9; Miller’s 
* Arch. f. Anat. u. Physiol.’, 1854, p. 60).—Jan. 28, 1921. 
