THE DEVELOPMENT OF ASTERINA GIBBOSA. 377 
sinus (gen. 7., woodcut 1); one of these branches runs in an oral 
direction down each side of the interradial septum. This 
septum is an ingrowth of the body-wall, which has by this time 
become marked, though its first beginnings date back to the 
end of the metamorphosis (Pl. 23, fig. 84). 
A section of one of these branches in an older specimen is 
given in Pl. 26, fig. 119). These genital branches are formed 
as the rachis reaches each interradial septum before it has 
formed a circle; in one specimen I have observed a rachis 
reaching only to the next interradius, and there giving off one 
genital branch. Figs. 120 and 121 (taken from the same 
specimen as fig. 119) show the first rudiments of the genital 
organs. The branch of the rachis ends in a swelling accom- 
panied by a dilatation of the aboral sinus, and we see the begin- 
ning of aseptum tending to shut off the main aboral sinus from 
this dilatation. This septum was first described by Cuénot (8), 
and in it the genital duct is formed. This is shown in fig. 123, 
taken from the oldest specimen I examined, in which R equals 
3:7 millimetres. We see that the genital duct is formed by 
a core of primitive germ cells burrowing its way through the 
body-wall. Fig. 122, from the same specimen, shows the con- 
tinuity of the rachis and the ovary. We notice also the forma- 
tion of follicles from the indifferent germ cells. 
We are now in a position to compare the arrangement of 
the ovoid gland and genital rachis and their accompanying 
spaces in Amphiura squamata with that found in Asterina 
gibbosa. In the former I described the genital rachis issuing 
from the oral end of the gland and accompanied by three 
spaces, which I named sinus a, sinus 6, and sinus ¢ (PI. 25, 
fig. 112), This figure is a diagram of a section parallel to the 
long axis of the stone-canal. Fig. 111 is a diagram of a 
similar section of Asterina, but it is not quite accurate, since it 
shows both the ovoid gland and the stone-canal, and these two 
structures do not lie in the same radial plane in Asterina. 
In order to avoid obscuring the opening of the stone-canal into 
the axial sinus, it is necessary to indicate part of the ovoid 
gland by dotted lines. 
