482 RECENT BRACHIOPODA chap. 



body to two-thirds of this length. The larvae are of a pinkish 

 red coloiu', with eye-spots of ruby red. Their colour renders 

 them diflicult to discern when they are swinnning over the red 

 coralline rocks upon which they frequently settle. After swim- 

 ming about for a few hours the larva fixes itself finally, 

 apparently adhering by some secretion produced by the stalk 

 segment. The folds of the second or body segment then turn 

 forward over the head, and now form the ventral and dorsal 

 mantle folds ; these at once begin to secrete the shell on their 



Fig. 320. — Stages in the development of the larva of Terehratulina septentrionalis. (After 

 Morse.) The youngest larva has two segments, a third then appears, the larva 

 then fixes itself, and the second segment folds over the first and develops bristles 

 round its edge. 



outer surfaces. The head with its eye-spots must l)e to some 

 extent absorbed, but what goes on within the mantle is not 

 accurately known. The setae drop oif and the tentacular arms 

 begin to appear as a thickening on the dorsal lobe of the mantle. 

 They are at first circular in outline. The various changes which 

 the larva passes through are well illustrated Ijy Morse for Tere- 

 hratulina, which spawns at Eastport, Me., from April till August. 

 The different stages are represented in outline in Fig. 320, taken 

 from his paper. 



Habits 



There is little to be said about the habits and natural history 

 of the Brachiopoda. When once the larva has settled down, the 

 animal never moves from the spot selected ; occasionally it may 

 rotate slightly from side to side on its stalk, and from time to 

 time it opens its shell. As so frequently is the case with sessile 

 annuals, the sense organs are reduced to a minimum, the eyes of 

 the larva disappear, and the only communication which the 



