SEA MUSSEL MYTILUS EDULIS. 



PRVSt ARV PdGStARV 



197 



184 Oes Dis f > \ 185 : > jfrT>! r 



L VI AAd An Tt1 , K *£ ' E ' L ' 



PAd BrF Oes VL AAA 



CG E PdG St PRet 



111 'i 



VI— 



AAd—V 



BrF K 



Fig. 184.— Transparent preparation of a larva, 0.274 by 0.260 mm., with -well-developed anterior adductor muscle, AAd, 

 and posterior adductor muscle, PAd. Liver, Z., and prismatic cell or dissoconch, Dis, just appearing. ARV, anterior retractor 

 muscle of velum; Oes, oesophagus. PRV, posterior retractor muscleof velum; St, stomath; VI. velum. 



Fig. i8<;.— Transparent preparation of a larva, 0.360 by 0.260 mm., showing fir?t appearance of foot. Ft; four branchial 

 filaments, BrF; eye. E; pedal ganglion, PdG; posterior retractor muscle of foot and byssus, PRet; and kidney, K. An, anus; 

 R, rectum; other abbreviations same as in fig 184. 



Fig. 186.— Transparent preparation of a larva, 0.385 by 0.329 mm., showing first appearance of cerebral ganglion, CG; 

 visceral ganglion, VG; otocyst, Ot; pericardium, P; and genital gland, G. The velum is degenerating, the anterior adductor 

 muscle is reduced in relative size, and the foot has undergone considerable growth. Other abbreviations same as in figs. 184 

 and 185. 



