198 



BULLETIN OF THE BUREAU OF FISHERIES. 



PRet G St 

 PAd\ R i P \PdG 

 Ot 



Dis VPC K Ft Pds 



St RI DI P K PRetPAd 



~^f^-BrF 



CG PdG ByT 



Fig. 187.— Transparent preparation of a young mussel showing relation of prodissoeonch, Pds, or larval shell, to dissoconch, 

 Dis, or adult shell. Anterior retractor muscle, A Ret, beginning of the labial palps, LP, and commissural nerve, VPC, appear 

 at this stage. The velum has degenerated and disappeared. Other abbreviations same as in figs. 185 and 186. 



Fig. 1 88. —Transparent preparation of a young mussel, 0.72 mm. long, showing the prodissoeonch. Pds, which is destined 

 to cover the umbo, the well-developed liver which has come to envelop the stomach, St, completely; the looping of the intes- 

 tine to form the direct intestine, DI, the recurrent intestine, RI, and the terminal intestine, 77. Byssus threads, ByT, extend- 

 ing from byssal gland, are present for the first time, and the kidney, K, pericardium, P, and gills, BrF, show considerable 

 advance in development over the previous stage figured. Other abbreviations same as 111 figs. 1S5, 1S6, and 187. 



