008 ANNIE MATTHEWS. 



never progressed beyond this stage, the specimens reared in Plymouth 

 continued to grow and develop, and are still doing so, although very 

 much below normal size, judging by specimens of this year's mussels 

 brought in from outside. The valves gradually assumed a shape rather 

 like a minute edible cockle, and about July 22nd, a purple colour — the 

 beginning of the prismatic shell substance — appeared at the edge of 

 the valves, behind the velum, and extending to the posterior edge of 

 the shell. The smallest individual in which the prismatic shell sub- 

 stance was visible measured '21 mm. long x -19 mm. high. The larvae 

 still swam with the velum and the foot was growing rapidly in size. 

 The eye spot was present and five gill filaments, and the valves 

 measured "31 mm. long x '24 mm. high. From now onward the larvae 

 grew at varying rates, some fixing by a byssus, while many others 

 remained unattached and much smaller, creeping about the jar. The 

 purple colour gradually extended over the valves, fading at its edges 

 into brown. On August 6th the foot had become very long, thin, and 

 active, the gill cilia were long and powerful, and the velum was 

 decreasing slowly in size. Later the foot was frequently used as a 

 creeping organ, and on August 15th I drew one specimen that could 

 both swim with the velum and creep with the foot ; it measured "29 

 mm. high x '32 mm. long, and had six gill filaments. A similar 

 specimen measured '32 mm. high x -38 mm. long, so that the young 

 mussel ceases to swim at a much later stage than the individual Wilson 

 saw (see Wilson, loc. cit.). 



From time to time more Nitzschia was added to the jars as food, and 

 the outside water renewed, in which they lived. 



Other specimens drawn on the same day had lost the large velum 

 and the powder of swimming, and were crawling with the long tongue- 

 like foot about the glass jars. Measured specimens were : — 



•35 mm. high x "413 mm. long, witli 5 gill filaments. 

 •385 „ x-46 „ „ 8 



•41 „ X -574 „ „ 10 



In the last individual the shell resembled a minute adult shell, being 

 much thicker and of elongated oval shape, and dark blue in colour. 



On August 27th most of the young mussels were crawling about the 

 jar, many near the water surface, the largest measuring ^74 mm. high 

 Xl*16 mm. long, with 15-16 gill filaments. The eye spot was still 

 visible through the shell. During September they attached themselves 

 to the glass at various levels — some at the water surface — by a delicate 

 byssus, all but one being fixed by October 4th. When removed 

 forcibly they soon refixed. About October 15th the jars were aerated 



