in the Fish Gallery of the Indian Museum. 9 



exhibited, are types of free-swimming Tunicates that 

 differ considerably from the simple fixed Ascidian. In 

 Salpa the branchial sack and the peribranchial cavity 

 form one continuous space, and the branchial and atrial 

 openings are at opposite ends of the body. This is a 

 special modification for locomotion, the animal being 

 propelled forwards by the forcible expulsion, from the 

 atrial opening, of the water that has been drawn into the 

 peribranchial cavity : this is effected by the contraction 

 of muscular bands in the mantle. Thalia moves through 

 the water in the same way. 



AMPHIOXUS. 

 Lancelets. 

 [Case 4.] 



This curious little fish, of which spirit specimens are 

 shown in Case 4, is so small that its structure can only 

 be illustrated in a Museum by enlarged drawings and 

 diagrams. 



No. 1 is a drawing of an Amphioxus enlarged 18 

 times, No. 2 is a much more enlarged diagrammatic 

 drawing of a cross-cut through the fore-end of an 

 Amphioxus. No. 3 represents the mode of life of 

 Amphioxus. 



The species are of world-wide distribution in tropical 

 and temperate seas, one species being common enough 

 in shallow water along the Madras coast. They pre- 

 fer sandy bottoms into which they can burrow, leaving 

 only the fore-end of the body exposed. In this position 

 they breathe and feed almost exactly in the manner of 

 the Ascidians, drawing through the mouth, into a 

 capacious pharynx, currents of water that contain 

 oxygen and minute particles of food. The water passes 

 through slits in the wall of the pharynx into a special 

 2 



