SPICULES OP SYNAPTA AND AURICULARIA LARVA. 509 



Fig. 25. — Side aspect of the anchor-handle and plate-base to show the joint 

 formed between the two. 



Fig. 26. — The problematic bodies fouud in the body-wall. 



The Development of the Auricularian Wheel-Spicule. 

 Fig. 27. — The initial granule in the syncytium. Its proximity to the body- 

 wall is indicated. 



Figs. 28 — 30 illustrate the growth of this granule (surface aspect). 



Fig. 31. — Tiie plate-like form which this granule assumes and the clustering 

 of the nuclei on its inner aspect (the aspect remote from the wall). 



Fig. 32. — The plate or dish in side view. The inner position of the cluster 

 of nuclei is well shown. 



Fig. 33. — Plate viewed from its inner aspect. 



Fig. 34. — Lateral aspect of full-sized plate. 



Fig. 35. — Plate viewed from its outer aspect (nuclei situated on its remote 

 side). The edge of the plate is crenate — the first indication of the spokes. 



Figs. 36 — 38. — Plate in all cases viewed from its inner aspect (nuclei on the 

 near side). The formation of the spokes and the corresponding distension of 

 the scleroplasm of the syncytium is shown. The nuclei with their accompany- 

 ing scleroplasm lie in the concavity of the plate. 



Fig. 39. — The spokes extend circumferentially. 



Fig. 40. — The felly of the wheel formed. The entire spicule is enveloped 

 by the scleroplasm. 



Fig. 41. — The wheel viewed from the side in optical section showing the 

 " eggs-in-a-basket " appearance. 



Fig. 42. — One of the calcareous globes of the Auricularia larva with its 

 enveloping syncytium situated in a shallow pocket of the body-wall. 



VOL. 51, PART 3. — NEW SERIES. 38 



