506 W. WOODLAND. 



(4) The situation of the heavy wheel and globe spicules at 

 one (the lower) extremity of the larva determines the position 

 which the larva assumes in the water — the spicules weight 

 the larva. 



Note on a Cukious Type op Siliceous Spicule. 



The curious spicular structure represented in text-fig. 6 was 

 found inserted for a short distauce into the bod}'^ of one of the 

 Auricularia larvcS which I examined. As it is not doubly 

 refractive under the polariscope^ I conclude that it is siliceous. 

 It is well clothed in a thick layer of scleroplasm containing 

 numerous nuclei. Being quite unable to identify this spicule 

 I should say that it is probably a freak. 



Literature. 



1. CuuN, C. — "Die Bilduus der Skelettheile bei Echiiiodennen," 'Zuol. 



Anzeig.,' vol. xv, 1892 ; translated iu 'Ann, Mag. Nat. Hist.' (G), vol. 

 ii, 1893. 



2. Herouaud, E. — " Sur uiie Loi de Formation des Corpuscules Calcaires et 



sur rHomoIogie qui existe entre ces Corpuscules cliez Ankyroderma et 

 Synapta," 'Bull. See. Zoo). France,' vol. xxvii, 1902. 



3. JIekouaud, E. — " Rechcrches sur les Holothuries des Cotes de France," 



' Tiicses,' Paris, 1890. 



4. OsTEiiGKEN, Hj. — " Ucbcr die Function der Ankerformigen Kalkkorper 



der Seewalzeu," ' Zool. Anzeig.,' vol. xx, 1897. 



5. Semon, K. — "Eeitriigc zur Naturgeschichte der Synaptiden des Mittcl- 



meers," ' Mittlieii. Zool. Stat. Neapel.,' vol. vii, 1887. 



6. Semon, 11. — "Die Entwickelung der Synapta digitata, und ilire Bedeu- 



tung fiir die Phylogeuie der Ecliinoderiucn," ' Jena Zeitscli.,' Bd. xxii, 

 1888. 



7. Woodland, \V. — "Study IV. The Scleroblastic Development of the 



S|)icules iu Cucumariida;; with a Note relating to the I'lale-and-anchor 

 Spicules of Synapta inhasrens," 'Quart. Journ. Micr. Sci.,' vol. 

 xlix, 190G. 



8. Woodland, W. — "A Preliminary Consideration as to the Possible Factors 



concerned in the Production of the Various Forms of Spicules," op. 

 cit., vol. li, 1907. 



