CHORDATA 233 



once, and it is from this specimen (now in the Guernsey 

 Museum) that I am able to give the length. 



It is tolerably frequent in the Channel Islands,at Chausey, 

 and the Minquier reefs. As to its localities on the English 

 shore, I have no data, but it must be pretty well distributed, 

 for its larval form (Tornaria) is frequent among the minute 

 organisms that live at, or near, sea surface, and which are 

 collectively termed " Plankton." 



The distinction between Balanoglossus proper and 

 Ptycliordem is in some details in development ; the latter 

 showing the Echinoderm resembling larval stages, the 

 former having a more direct method of development. The 

 former is also the more northern, the latter the southern 

 form (see excellent article on Balanoglossus in " Encyclo- 

 paedia Britannica "). 



The Tunicata or Ascidians. The first of these titles is 

 applied to the class of animals before us on account of 

 their being enveloped in a more or less leathery " tunic " 

 or test, the second on account of their form, which bears 

 some resemblance to an ancient leather wine-bottle 

 (Ascis). 



A VGTJ great deal of interest attaches to the tunicates, as 

 they are believed, by the authorities most competent to 

 decide, to be allied to the forms from which the verte- 

 brates have evolved. 



In outward appearance an ascidian seems to be of very 

 lowly organisation, fixed (the greater number of species) 

 to rock, stone, or sea-weed, with no power of movement 

 beyond, to a slight extent, the protrusion and retraction 

 of the slight tubes which border the openings to the body 

 " inhalant " and " exhalant " apertures. Reference to 

 the diagram (Fig. 102) will help readers to understand the 

 general plan of their anatomy. In function they closely 

 resemble the lamellibranch molluscs, the inhalant aperture 

 taking in, by means of the action of the cilia which line it, 



