EOKMS OF SPICULES. 77 



ray of young Sycon triradiates it is noteworthy that this 

 feature has been made use of to some extent by the organism, 

 since if the triradiates are rotated sufficiently (Study I, pp. 

 263 — 265) the large basally-directed rays afford extra support 

 and enable the sponge to assume a more erect posture. Thus 

 the shapes of spicules are not only in part determined by the 

 form of the organism, but the contrary is also the case. 



This large ray o£ the young Sycon triradiate is the only 

 instance apparently affording support to the theory of the 

 inheritance of spicule forms which I can at present call to 

 mind. But even if later evidence definitely proves the inherit- 

 ance of spicule forms to be a fact I shall not regret having 

 published a discussion which at the least illustrates the com- 

 plexity of the whole subject and suggests inquiry in more 

 than one direction. 



LiTEKATDKE. 



1. Bidder, G. P. — "Tlie Skeleton and ClassiQcatiou of Calcareous Sponges," 



'Proc. Roy. Soc. Lond.,' vol. Ixiv, J 898. 



2. Bowman, J. H. — "A Study in Crystallisation," 'Journ. Soc. Chem, 



Industry,' vol. xxv (4), 1906. 



3. BiJTSCHLi, 0. — ' Mechanismus und Vitalismus,' Leipzig, 1901. 



4. "Einige Beobachtungeu iiber Kiesel- und Kalknadeln von Spon- 



gien," ' Zeit. wiss. Zool.,' vol. Ixix, 1901. 



5. Daibek, a. — ' Microskopie der Harnsedimeute,' Wiesbaden, 1896. 



5a. Dkeyek, F. — " Die Prinzipien der Geriistbildung bei llhizopoden, 

 Spongien und Ecliinodermen," 'Jena Zeitsclir.,' Bd. xxvi (N.F., Bd. 

 xix), 1892. 



6. Ebner, V. VON. — "Ueber den feineren Bau der Skelettbeile der Kalk- 



sclivvamme nebst Bemerkungen iiber Kalkskelete iiberliaupt," ' Sitzb. 

 Akad. Wien. Matb. Nat. CI.,' vol. xcv, 1887. 



7. Gautier, a. — "Du Mecanisme de la Variation des Etres vivants, etc.," 



in ' Hommage a M. Clievreul a I'Occasion de son Centeuaire,' 1886. 

 7a. Hackek, V, — " Ueber die biologische Bedeutung der feineren Struk- 

 turen des Radiolarienskelettes," 'Jena Zeitschr.,' Bd. xxxix, 1905. 



8. Hakting. — '"On the Artificial Productiou of some of the Principal 



Organic Calcareous Formations," ' Quart. Journ. Micr. Sci.,' N.S., 

 vol. xii, 1872. 



