512 Arthur E. Shipley 



35 mf\ , these rim from tlie small mass of liomogeueous siibstance at the 

 posterior end of the larva to the origiii of the folci : some fibres also pass 

 down between the two layers of the fold and are inserted into the ovai 

 mass of cells which secrete the setae. These muscles probably beeome 

 the adjustors of the adult. 



In the head segment, into which the alimentary canal extends but 

 a very slight distance, there is a small dump of cells, without the large 

 grauules characteristic of the other cells : this may possibly be a nerve 

 gauglion (fig. 35 /. ^) . 



When the larva has reached the stage just described, the fìlameut 

 connecting it with the w^alls of the brood pouch breaks , and the larva 

 escapes from the shell of the mother. In the ^vater it swims rapidly to 

 andfro, by the aid of the cilia, especially those long ones upon the edge of 

 the anterior segment, sometimes it stops and revolves rapidly on its long 

 axis. Freqnently it Stands ou its head for a considerable length of time. 

 It is extremely coutraetile and seldom retaius the same shape for any 

 length of time ; its head segment is turned rapidly from side to side, and 

 on approachiug any object, the body is often much shortened and the 

 setae are protruded in every direction. The length of the free swimming 

 larva fuUy extended is about 73 mm. though it freqnently contracts to 

 2/3 of this. 



The setae bave probably a defensive function : the color is also pro- 

 bably protective ; when the larvae are fixed upon a piece of red coralline 

 upon which they usually come to rest, it is very diftìcult to distinguish 

 them. 



After swimming about for a few hours the larva fixes itself ou a 

 piece of rock or some other object, by means of a secretion appareutly 

 supplied by the posterior segment. 



I bave not been able to follow the metamorphosis of the larva iuto 

 the adult ; the following description is taken from Kowalevskys article 

 mentioned above. 



When the larva is fixed, the fold which previously covered the third 

 »segmenta gradually turns forward and grows over the head »segment« : so 

 that the columnar cells previously inside beeome the outer layer. This 

 fold forms the mantle and it begins to secrete the shell. The head be- 

 comes spherical, and the eyes persisi. The digestive canal becomes 

 round and is produced into the head segment , this part probably form- 

 ing the Oesophagus. The lophophore begins to appear as four pro- 

 jections directed inwards, on a thickening of the dorsal lobe of the 

 mantle near its border. This thickening soon takes the form of a ridge; 



