A Guide to the Zoological Collections 



in accordance with the classification of Ray Lankester, 

 be regarded as an independent branch of the Vertebrate 

 stock. 



It is convenient to exhibit in the Fish Gallery certain 

 more or less degraded marine animals in which the 

 vertebrate affinities are, at least in adult life, obscured. 

 These are the Ascidians [Tunicata) and Balanoglossus. 

 They have not the slightest external resemblance to 

 ordinary vertebrate animals, and in the case of the 

 worm-like Balanoglossus the vertebrate affinities are not 

 undisputed ; but the Tunicata are very reasonably con- 

 sidered to belong to the Vertebrate phylum principally 

 on the grounds (i) that their larva — though not usually 

 the adult — has a notochord or primitive foundation of a 

 backbone, (2) that at least the main mass of the nervous 

 system lies to the dorsal side of the level of the noto- 

 chord, and (3) that the front part of their digestive tube 

 is peculiarly modified for breathing. 



It must be remembered that Balanoglossus and the 

 Ascidians are exhibited in the Fish Gallery simply for 

 convenience : they would be out of place in either of the 

 Galleries of Invertebrates, and they are not, from a 

 Museum point of view, important enough to have a 

 gallery to themselves among the Vertebrates ; although 

 from many other points of view they are among the 

 most important and most interesting of all animals. 



BALANOGLOSSUS. 



[Case 1.] 



In external appearance, as in mode of life, the adult 

 Balanoglossus resembles certain marine worms. Its 

 larva in certain species, of which much enlarged figures 

 are shown in Case 1, resembles certain Echinoderm 

 larvae. 



