in the Fish Gallery of the Indian Museum. 



It has been classed both with the Worms and near 

 the Echinoderms, but certain very suggestive peculiari- 

 ties of its structure have lately led the most advanced 

 zoologists to remove it to the Vertebrate phylum. 



It is not possible to discuss all these peculiarities 

 here, but one of the chief of them, namely the essentially 

 vertebrate ground-plan of the breathing-mechanism, is 

 seen in the diagrams, specimens and model in Case i. 

 The general correspondence of the plan of the breathing 

 arrangements of Balanoglossus with those of certain 

 branchiate vertebrates is remarkable. This correspond- 

 ence would not of itself justify the inclusion of Balano- 

 glossus in the Vertebrate phylum, were it not that the 

 essentially vertebrate notochord and dorsal nerve-tube 

 are also represented, though obscurely and imperfectly, 



in Balanoglossus. 



The enlarged drawings and diagrams in Case i will 

 explain the structure of the animal. 



No species of Balanoglossus has been found in these 



seas. 



TUNICATA. 



Sea-Squirts. 



[Cases 2-3.] 



Owing to the fact that in the more familiar members 



of the group the body wall forms a muscular mantle 



and secretes a thick protective test, the Tunicates were 



originally classed with the Mollusca. 



But the knowledge that the larva of many Tunicates 

 has a notochord in the posterior part of its body, or tail, 

 and a dorsal nervous system (brain, etc.), formed on the 

 Vertebrate plan ; and that there are certain small free- 

 swimming Tunicates that keep the larval tail and brain , 

 though somewhat changed, throughout life ; added to the 



