STUDIES IN SPICULE FORMATION. 557 
small contained nuclei usually aegregate both towards the 
point of the arm and towards the handle. A certain number 
of nuclei are also to be observed in the perforations of the 
anchor-plate, along the shaft, and on the bow. ‘There is also 
in every case a great concentration of protoplasm at the 
junction of the anchor with the plate, as shown. I have 
observed scores of spicules showing precisely the same 
features as those just described, and these are evidently 
constant for the adult spicule. Fig. 44 shows a similar 
spicule in side view. ‘The angles which the arms of the bow 
make with the shaft and which the shaft makes with the 
Trext-FIG. 4. 
anchor-plate can be easily observed. It would be interesting 
to ascertain whether or no the recurvature of the arms of the 
bow is at all due to a tractive action exerted on these by the 
possibly muscular strands of protoplasm just described. 
LITERATURE. 
1. Cuun, C.—‘ Die Bildung der Skelettheile bei Echinodermen,” ‘Zool. 
Anzeig.,” vol. xv, 1892. Translated in ‘Ann. Mag. Nat. Hist.’ (6), 
vol. ii, 1893. 
2. Geroup, J. H.—* The Anatomy and Histology of Caudina arenata, 
Gould,” ‘ Proc. Bost. Soc.,’ vol. xxvii, 1896. 
3. HERovarD, E.—“Sur la formation des corpuscles caleaires chez les 
Holothuries,” ‘Compt. rend. hebdom. Acad. Sci. Paris,’ vol. ev, 1887. 
4. ——— “Recherches sur les Holothuries des cdtes de France,” ‘ Théses,’ 
Paris, 1890. 
