508 W. WOODLAND. 



Pig. 10. — The fully-elongated shaft. The terminal knob (representing the 

 unelongated portion of the initial granule) is now extending laterally. The 

 axis is conspicuous at this stage. 



Fig. 11. — The fully-elongated shaft seen in a transverse section of the body- 

 wall. The external position of the majority of the nuclei relative to the shaft 

 is well shown. 



Fig. 12. — Adult shaft, in which the arms of the anchor are about half 

 formed, seen in a transverse section of the body-wall. In this figure there is 

 shown in the clearest manner the external position of the majority of the 

 nuclei, and the internal position of the half-dozen or so nuclei which have 

 migrated internally to form a separate cluster in this position. All stages of 

 this migration can be seen in the actual preparations. 



Fig. 13. — Spicule viewed from the internal aspect. A granule has been 

 deposited in the internally-situated cluster of nuclei. The formation of the 

 arms of the bow is distending the general syncytium in this region (formation 

 of the "patagia"). 



Fig. 14. — The granule is elongating on both sides in a direction transverse 

 to the length of the anchor-shaft. 



Fig. 15.— The same stage of growth of another spicule viewed in a trans- 

 verse section of the body-wall. 



Fig. 16. — Spicule viewed from the internal aspect. The granule has become 

 a distinct rod with rounded extremities and swollen centre. In this species — 

 S. inhasrens — it is, as remarked in the text, situated transversely to the 

 length of the anchor-shaft. 



Fig. 17. — The same stage in S. digitata. It will be noticed that in this 

 species the rod is siluated jiarallel with the shaft and not at right angles to it. 

 This difference between the two s|)ecies of Synapta is quite constant. 



Fig. 18. — S. inhscrens. The extremities of the transverse rod have 

 bifurcated. The " patagia " are well shown here. 



Fig. 19. — S. digitata. The extremities of the parallel rod have bifurcated. 



PLATE 30. 



Fig. 20. — S. inhrcrens. The bifurcated extremities of the transverse rod 

 have themselves bifurcated. The " patagia " are giving place to the " strands " 

 uniting the apices of the anchor arms and the handle. 



Figs. 21 — 23 illustrate the further formation of the plate and the proto- 

 plasmic strands with their aggregates of nuclei. 



Fig. 24 illustrates an anchor, in connection with which no plate has been 

 formed. 



