380 E. W. MACBRIDE. 
Cuénot brings to show that they escape by diapedesis into the 
axial sinus is quite insufficient. The cells of outer epithelial 
lining are not flattened but cylindrical, and I strongly suspect 
that he has mistaken their freely projecting ends for escaping 
amoebocytes; and I may remark that this curious outer 
epithelium shows its distinctive character from the time the first 
rudiment of the ovoid gland appears. Whatever its function 
may be now, there is no doubt that the ovoid gland was pri- 
mitively a part of the genital organ, and probably is a remnant 
of the arrangement of the reproductive cells before the radial 
symmetry was acquired. It is interesting to notice that it 
originates from the left posterior coelomic wall, whereas an 
analogous organ in Crinoids arises in the right or aboral ceelom, 
so that they are not strictly homologous. 
If Hamann is, as there is strong reason to suppose, right 
in stating that the primitive germ cells wander along the 
rachis into the genital organ, it seems very probable that, 
at any rate in the young adult, the ovoid gland is a centre 
of formation of the primitive germ cells; and its relation to 
the axial sinus may have to do with its aération, for it must be 
remembered that the pore-canal opens into the axial sinus, and 
the current in this is, as we shall see, inwards. In the fully 
grown adult it no doubt undergoes, to some extent, the degene- 
rative change noted above in the genital rachis of other genera. 
What the meaning of this change is, is very obscure. Obser- 
vations on the histology of the gland at different seasons might 
elucidate its meaning. 
Turning now to the stone-canal, we see, in fig. 118 (a section 
transverse to the axial sinus and stone-canal), the beginning 
of that curious T-shaped ingrowth which is so marked a feature 
of the stone-canals of Asterids, but which is much less developed 
in Asterina than in other genera. It is covered by short cilia, 
the rest of the epithelium bearing long flagella. 
Cuénot asserted that the stone-canal was a functionless rudi- 
ment, the current being neither outwards nor inwards, Ludwig! 
' Ludwig, “ Uber die Function der Madreporenplatte und des Steinkanals 
der Echinodermen,” ‘ Zool. Anz.,’ 1890, p. 377, 
