Therefore in Asterina gibbosa, as I have shewn it to be the case 
in Amphiura squamata, the genital cells are ultimately derived from 
the peritoneum. Asterina gibbosa thus shews the same origin for its 
sexual cells as Vertebrata, Annelida, and in fact all Coelomata. 
We are now in a position to compare the corresponding structures 
“found in Amphiura squamata with those just described. 
The axial sinus of Asterina gibbosa, into which the stone canal 
À opens, is obviously homologous te the »ampulla« of Amphiura squamata, 
which has the same relation though relatively less developed. I have 
called it sinus c therefore in Fig. 15. In both animals the peculiar 
cells of the dorsal organ are derived from the peritoneal, 
epithelium, but subsequently by a process of invagination become 
shut off from it. Hence, the so-called axial sinus (sinus 5) of Amphiura 
squamata corresponds to the canal in the dorsal portion of the »heart« 
of Asterina gibbosa. Finally the aboral sinus is homologous in the two, 
and originates in the same way: the undulating course which it pur- 
sues in Amphiura squamata is evidently conditioned by the curious 
way in which the abactinal surface has grown in between the actinal 
radii, in Ophiurids ; the madreporite and stone canal being thus forced 
round to the ventral side, whilst the aboral sinus is pulled out into 
5 interradial ventral loops. 
One word on Ludwig’s »haemal« system in Asterina gibbosa. 
… The radial haemal strands penetrate only for a very short distance into 
the septum dividing the radial perihaemal canal. In the septum sepa- 
rating the inner and outer oral perihaemal rings, there is a strand of 
- cells continuous with and similar in character to, the inner cells of 
the dorsal organ. These therefore are peritoneal in origin. Well pre- 
| served specimens shew at once that we have to deal with a strand 
of cells and not with a vessel. 
The axial sinus (c) exists already in the metamorphosing larva. 
| Of its origin and significance, as well as of the development of the 
_ whole perihaemal system I hope to be able to give an account in my 
+ complete paper. 
| 
a 
» 
f 
i 
In conclusion I have to express my warm thanks, to Cav. Salva- 
tore Lo Bianco who spared no pains in obtaining for me the rare 
- and valuable postlarval stages on which my work has been principally 
based. 
The Morphological Laboratory Cambridge, March 24 1893, 
