132 Dr Grant's Observations on the Structure 



that some part of their white translucent base (fig. 28. c, 6.), is 

 in contact with the glass ; and this part has not only the power 

 of adhering firmly to the surface, but that of spreading itself 

 outwards, so as to extend the whole ovum into a thin transparent 

 convex circular film. During the expanding of the base, the 

 cili» are still observed in rapid motion on the upper part, and 

 propelling particles of matter to a distance. ^They soon, however, 

 become languid, and, in the course of a few hours, they cease to 

 move, first at a particular part, and then gradually round the 

 whole circumference. When first completely expanded, the 

 whole ovum appears to consist of granular monade-like bodies, 

 with a iew spicula interspersed through the central parts, (fig. 

 29. part within d.). But within the space of twenty-four hours, 

 a beautiful transparent, colourless, and perfectly homogeneous 

 margin, has spread out round the whole ovum (fig. 29- 6.), 

 which continues to surround it during its future growth. And 

 although all visible ciliae have ceased to move, we still perceive 

 a cleared space around the ovum, and a halo of accumulated se- 

 diment, (fig. 29. c), at a little distance from the margin. The 

 spicula, which at first were small, confined to the central part, 

 and not exceeding twenty in number, now become much more 

 numerous and larger, and some of them even make their appear- 

 ance in the thin homogeneous margin (fig. 29. h.). The spicula 

 make their appearance completely formed, and do not seem after- 

 wards to increase their dimensions. I have never observed a 

 spiculum in the act of making its appearance, but have thought 

 that I perceived a lineal arrangement of the monade-like bodies 

 in the interior of the ovum, where the spiculum afterwards start- 

 ed into being. When two ova, in the course of their spreading 

 on the surface of a watch-glass, come into contact with each 

 other, their clear homogeneous margins unite without the least in- 

 terruption, they thicken and produce spicula : in a few days we 

 can detect no line of distinction between them, and they continue 

 to grow as one ovum. Cavolini long since observed, that, when 

 two adult specimens of the S. rubens. Pall, growing on the side 

 of an earthen vessel, came into contact with each other, they 

 grewtogether and formed an inseparable union, (Abhand. p. 126.) 

 In a few weeks after an ovum has fixed, the spicula assume the 

 appearance of fasciculi ; at particular places towards the centre 



