a.po 



Figure 340. — Fully developed larva of 0. edulis viewed from the right side with velum and foot at the ventral side in 

 the uppermost position, typical for swimming. According to Erdmann, 1935. a. — anus; ab.c. — aboral belt of cilia; 

 ant. ad. — anterior adductor muscle; a.p.o. — apical sense organ and ganglion; b.g. — byssus gland; cr.s. — crystalline 

 style sac; d.div. — digestive diverticula; e. — esophagus; ey. — eye; f. — foot; f.r. — foot retractor muscles; g. — gill 

 rudiment; g.sh. — gastric shield; h.r. — heart and kidney rudiment; int. — intestine; m. — mouth; m.c. — mantle cavity; 

 p.g. — pedal ganglion; post. ad. — posterior adductor muscle; r. — rectum; r.v. — velar retractor muscles; st. — stomach; 

 stc. — statooyst; v. — velum; v.g. — visceral ganglion. 



rectum. The gill ruduiient (g.), located between 

 the base of tlie foot and heart rudmient, consists 

 of a series of short, tubular channels. The pedal 

 ganglia (p.g.), a round structure at the base of 

 the foot, disappear with the dissolution of the 

 foot. The visceral ganglion (,v.g.) appears in its 

 permanent position at the ventral side of the 

 posterior adductor. The larval sense organs com- 

 prise a pair of statocysts (stc.) in the foot tissue 

 and a pair of dark pigmented eyes (ey.) which 

 develop toward the end of larval life. Their pres- 

 ence in the free-swimming larvae indicates the 

 approaching of setting and metamorphosis. 



The nervous system of the larva, shown dia- 



grammatically in figure 341, is more complex than 

 that of the adult oyster. It contains the pedal 

 ganglia (ped.g.), which are absent in the adult; 

 the pleural ganglia are present as a separate 

 structure and are connected to the statocysts 

 (syc.) and eyes, which disappear without a trace 

 during metajnorphosis. The visceral ganglia 

 (visc.g.) of the larvae are less conspicuous than in 

 the adult. All these organs are obviously neces- 

 sary to a free-swimming organism, and some of 

 them disappear with the loss of locomotion and 

 the change to a sedentary mode of living. 



The anatomy of the fully developed larva of 

 C. viryinica is smiilar to that of 0. edulis. Figure 



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