THE DEVELOPMENT OF ASTERINA GIBBOSA. 309 
which is the axial sinus, embedded in the wall of which is 
the stone-canal (Pl. 25, figs. 110—118). This axial sinus 
ie tle 
ph. 1.2, &e. Rudiments of the outer perihemal ring. a‘, Axial sinus and 
its outgrowth the inner perihemal ring. a. Aboral sinus. gev.r. 
Genital rachis. 
was supposed to open at its upper end into an aboral periheemal 
ring or pentagon, from which in each interradius two canals 
branched off to go to the genital organs. As is well known, 
these spaces were called “perihemal” by Ludwig (10), because 
he imagined that he had discovered the true blood-system in 
the form of curious tracts of tissue embedded in the longitudinal 
septa of the radial canals, and in the septum separating the 
two circular canals. He further supposed that that curious 
