SPICULES OF SYNAPTA AND AURICULABIA LARVA. 503 



necessary for the envelopment of the entire spicule is effected 

 by the growth of the spicule itself, the spokes, e. g. pushing 

 out the peripheral scleroplasm before them as they increase 

 in length. The syncytium no more enlarges itself for the 

 accommodation of the spicule, as Chun imagines, than an 

 adipose tissue corpuscle swells out to make room for the 

 secreted oil. 



Unlike Chun I have not observed that " corresponding with 

 the centrifugal process of the calcification, the majority of the 

 cell-nuclei also separate from one another in a centrifugal 

 direction.^' On the contrary, in the Auriculariae observed by 

 me, they do not desert the nave portion of the wheel. In 

 short, the development of the Auricularian wheel resembles 

 that of all other echinoderm spicules in that they are endo- 

 plastic deposits, the form of which bears little or no relation 

 to the disposition of the nucleus or nuclei. The study of 

 spicule formation clearly shows that the proximity of a 

 nucleus is not essential to the deposition of skeletal material 

 at any given point, and that deposition goes on in any given 

 region of a cell independently of the distance of the nucleus 

 or nuclei from that region. Nuclear material is in all proba- 

 bility a sine qua non where spicular deposition is con- 

 cerned, but, as in the political constitution, the exact position 

 of the governing centre is of little or no account in regulating 

 the activities of the various areas governed — work proceeds 

 in all quarters, and not merely in the vicinity of the nucleus 

 or parliament as the case may be. 



The development of the calcareous globes of the Auricularia 

 is quite simple. The globe originates as a granule in the 

 syncytium and simply increases in diameter by the uniform 

 deposition of calcareous matter on its surface. The globe 

 protrudes on the surface of the body-wall, at least half of its 

 area being in contact with the wall, and the nuclei of the 

 syncytium, probably in consequence of the contact, become 

 restricted to the surface of the internal hemisphere (fig. 42). 



