205 



An ooecial valve (figs. 3 a, 3 h, 3 i, 3 k) is a strongly arched, rather thin- 

 walled, bilaminar structure, the two layers of which are joined in the entire free 

 margin of the valve. Its outline is like the one half of a transversely cut bean, 

 and its straightly cut-off, proximal margin, which is in contact with the corre- 

 sponding margin of the cryptocyst-bearing surface of the gonozooecium, forms on 

 one side a right angle (towards the colony) and on the other side an obtuse 

 angle with the curved line, that forms the further delimitation of the valve. The 

 two valves are only connected with the gonozooecium in the periphery of the 

 two elongated openings at its margin, and corresponding with these is a similar 

 opening in the proximal margin of each valve. This connection is brought about 

 by means of a slightly chitinized portion, which permits the valves to bend out- 

 wards when the larvae are to be set free and appears on either side as a trans- 

 versely oval, translucent spot, bounded proximally (towards the gonozocEcium) by 

 a slightly curved part of the separating ridge of the cryptocyst distally to the 

 lateral pore-chamber (fig. 3 k) and distally by a curved thickened part of the 

 ooecial valve (the » proximal arch«), which sends upwards two narrow, curved 

 belts, originating from a partial fusion of the two layers of the valve. The inner 

 surface of the valve also presents a chitinized portion proximally, which is 

 bounded distally by a calcareous thickening connected with the just mentioned 

 proximal arch. This thickening is placed lower, so that on exartiining the inner 

 surface of the valve the basal arch will be seen projecting above it. The few 

 younger stages (3 b, 3 k) I have found of such an ooecium show, that the two 

 ooecial valves begin as two small, rounded, widely separated plates, situated im- 

 mediately above the elongated openings in the margin of the gonozooecium, and 

 that it is only later that they meet at their margins and exjjand over the entire 

 periphery of the cryptocyst-bearing surface. Such a very young stage of ooecium 

 has also been figured by Busk. 



It still remains to give a morphological explanation of this singular form of 

 ooecium. As the gonozooecium has no horn-like spines, which appear in all the 

 other zooecia, it is an obvious conclusion that the two hollow ooecial valves may 

 have arisen by a transformation of these spines, and in my preliminary state- 

 ment^ I have taken this view of the matter. However the conclusion cannot stand 

 a closer examination. Besides the distal pore-chamber, situated in the side of the 

 gonozooecium turned away from the colony, the gonozooecium has further two 

 elongated lateral pore-chambers (figs. 3 a, 3 k), situated immediately on the proxi- 

 mal side of the place where the valves are attached, and the two elongated 



' 56, p. 16. 



