502 W. WOODLAND. 



with eacli other to produce the few spicules found ; probably 

 both processes occur. The syncytium of the Auricularia 

 larva differs from the syncytium of Synapta in that in the 

 former each nucleus is almost entirely surrounded by a dis- 

 tinct layer of protoplasm, i.e. cell-outlines are to a large 

 extent visible, each nucleus occupying a distinct subspherical 

 portion of the syncytium, whereas in the latter the individual 

 cells are so fused together as to constitute merely a mass of 

 protoplasm containing numerous nuclei. The syncytium of 

 the Auricularian spicule contains, in the specimens I studied, 

 from five to nine nuclei. 



The spicule first appears in this syncytium as an endoplastic 

 spherical granule (figs. 27, 28), which is usually situated on 

 the side of the syncytium next to the adjacent body-wall 

 (not indicated in most of the figures). This granule flattens 

 and gradually becomes disc-shaped with a slightly concave 

 internal surface, the centre of which at first bears a slight 

 eminence, and a convex external surface (figs. 31, 32) which 

 is in contact with the body-wall. All the scleroblasts (i. e. 

 the nuclei with their subspherical masses of protoplasm) are 

 situated on the concave side of the disc, i.e. remote from the 

 body-wall, and are clustered together (figs. 31, 32, 34), though 

 of course the entire disc (and all later stages of the spicule) is 

 enveloped by the scleroplasm. The next step in the develop- 

 ment is the formation of processes (variable in number, rang- 

 ing from about fourteen to eighteen) at the margin of the 

 disc or nave of the future wheel (fig. 35), and these processes, 

 which vary in number in different spicules, elongate, and 

 ultimately form the spokes (figs. 36-38). By the develop- 

 ment of these spokes (the exact shape of which can be seen 

 in fig. 41) the convexo-concave disc assumes more the shape 

 of a cup. Finally these spokes, by lateral extension, join up 

 to form the felly of the wheel (figs. 39-41). The adult 

 structure then, as shown by the figures, forms a cup-shaped 

 structure, in the concavity of which are lodged the sclero- 

 blasts — somewhat like eggs in a basket (fig. 41). 



In every case the extension of the scleroplasm which is 



