52 W. WOODLAND. 



well several small spicules situated within one cell. No 

 nuclei are shown in any of these figures. In the first place I 

 may say that I do not remember ever having observed more 

 than one spicule contained within a single cell; and secondly, 

 that the above authors are greatly mistaken in supposing the 

 outline of the scleroblast containing the adult spicule to be 

 spherical. A scleroblast containing a spicule only remains 

 spherical when the contained spicule is small compared with 

 the original size of the cell (microscleres of some siliceous 

 sponges and the young stages of larger spicules e.g.) ; Avhen 

 as in Leptoclinum or Didemnum, the spicule is many times 

 larger than the original scleroblast, this latter necessarily 

 becomes distended and envelops the entire spicule with a thin 

 layer of scleroplasm, Avhich of course assumes the shape of the 

 spicule. If the spicules are too hastily decalcified it is quite 

 conceivable that the evolution of gas, being coincident with 

 the disappearance of the mass of the spicule, inflates the 

 scleroblast, and thus causes it to artificially assume a spherical 

 shape; indeed, I have some evidence that this is liable to 

 occur. Decalcification by means of the acid-alcohol used in 

 the borax-carmine method is very slow, and the scleroplasm 

 I'etains its stellate form, though the spicule has largely or 

 wholly disappeared. 



LiTEEATUEE. 



1. GiAKD, A. — " Recberches sur les Ascidies Composees ou Synascidies," 



'Archiv Zool. exper.,' t. i, 1872. 



2. Heudman, W. a. — " The Presence of Calcareous Spicula iu the Tuiii- 



cata," 'P. Geol. Soc. Liverpool,' 1884-85. 



3. Heusciier, J. — "Zur Anatomic und Histologic der Proncomeuia 



sluiteri, Hubreclit," 'Jena Zeitschr.,' Bd. xxvii, 1892. 



4. HuBRECHT, A. A. W. — "Proneomenia sluiteri; with Remarks upon 



the Anatomy and Histology of the Amphineura," 'Archiv fiir Zoologie," 

 Suppl., Bd. i, 1881. 



5. KowALEVSKY, A. O., and Marion, A. F. — "Contributions a THistoire 



des Solenogastres ou Aplacophorcs," 'Annales du Musee d'Histoire 

 Naturelle de Marseille,' "Zoologie," t. iii, 1887. 



