378 E. W. MACBRIDE. 
Comparing figs. 111 and 112 we see that the axial sinus of 
Asterina is represented in Amphiura by sinus ¢, the so-called 
“ampulla.” The aboral sinus (ad, fig. 111, sinus a, fig. 112) 
is also obviously homologous in both. 
[Since my paper (14) was published, and since the present 
work was sent in for publication, I have made a careful re- 
examination of my sections of Amphiura squamata, and 
have arrived at amore complete comprehension of the structure 
and development of the ovoid gland and the neighbouring 
spaces in that animal. The space marked sinus 0’ (fig. 112) 
is not, as I formerly supposed, a part of sinus 4, but is quite 
distinct. Sinus 0’ probably represents the right hydroceele ; 
it is already present in the youngest specimens I examined. 
Sinus 5* is a portion of the ccelom shut off by the outgrowth of 
a flap of peritoneum; from the inner wall of this sinus the 
cells which at the same time give rise to the ovoid gland and 
to the genital rachis take their origin; it is obviously homolo- 
gous to the cavity of the invagination of the primitive germ 
cells (pr. germ inv., figs. 110 and 111), only in Asterina this 
space disappears.—December, 1895. | 
We observe that the arrangement in Amphiura might be 
obtained from that in Asterina by rotating the stone-canal and 
accompanying structures outwards and downwards through an 
angle of 180°. That this is what has occurred in phylogeny 
is indicated, not only by the fact that in the young Amphiura 
the madreporite is near the edge of the disc and the stone- 
canal almost horizontal, whereas in the adult the madreporite 
is situated far in towards the mouth on the oral surface, but 
also by the curious undulating course of the genital rachis, 
which is aboral in the interradii and oral in the radii. This 
points to the conclusion that the aboral parts of the interradii 
* In my paper on this subject (14) sinus Jis referred to as the axial sinus— 
it was formerly supposed to be continuous with sinus ¢, though Ludwig knew 
this was not so. At that time the meaning of the axial sinus in Asterids 
which Bury first suggested (2) was not generally known, and his interpreta- 
tions were not accepted, and hence two different spaces were called axial 
sinus, one in Asterids and the other in Ophiurids. 
