12 



The broedinn season o: . irnhriata and i', i>orvGf;ica 

 seems to extend, tliroxagh the v/arni season. I i.uve round 

 ripe sexual products of both species i'rom early in May 

 till the middle of August. At the latter time there seem- 

 ed no abatement in their development. As v/ill be describ- 

 ed later, individuals became sexually mature in a month 

 after they have attached, and those which attach in August 

 must bear ripe sexual products later in the season, so 

 that the breeding season seems to extend throiagh the sum- 

 mer. 



Attachment of the Larva.- During its free mode of life, 

 the "ship-v.'orm" larva has gradually developed into the 

 typical larva of marine Lamellibranchs. There is a shell 

 into v/hich the v;hole creature may be wi thdravm foi- protec- 

 tion; a large svyimming organ, the velum, by means of which 

 the larva swims freely in the v/ater; a long, active foot, 

 by means of which it crawls actively over sui'faces. At 

 the end of this larval development, in fact, the "T'^ip- 

 worTO"larva is a typical small bivalve, except that it pos- 

 sesses the svrimming organ. 



Throughout the cummer (or at least from t'ay till 



