ANATOMY OF THE CLAM. 



247 



eggs as they are dis- 



gills, where the embryos in some species partially develop. 



Impregnation probably takes place within the branchial 



chamber, the spermatozoa being 

 swept in with the respiratory 

 current, and coming in contact 

 with tlie 

 charged. 



An excellent general view of 

 tlie relation of parts to the 

 body -walls and shell may be 

 seen by hardening a clam, or 

 better a fresh -water mussel, 

 Unio (see Fig. 161, D) in alco- 

 hol, and then making trans- 

 verse sections. A section can 

 be floated oft' in water and ex- 

 amined with a lens. The jDer- 

 fect bilateral symmetry of parts 

 will thus be seen. 

 The above description will answer for the majority of lar 



Fig. 166. — Pedal ganglia and oto- 

 cyets (ears) of the clam, magnified 10 

 diameters, d, pedal ganglia ; e, pedal 

 commisaures ; /, line of union of gan- 

 glia ; g, nerve from commissure to 

 muscles of foot ; h, auditory nerve ; i, 

 octocysfc ; k, nerves from ganglia to 

 the pedal muscles.— Drawn uy W. K. 

 Brooks. 



Fig. 16T. — Lima hians, flying through the water, its long numerous filameuts ex- 

 tended. — From Brehm's "' Thierleben. " 



mellibranohiate mollusks ; in the oyster (Osfrmi) or in Ano- 



