ANATOMY OF THE CLAM. 



227 



gills, where the embryos in some species partially develop. 



Impregnation probably takes place within the branchial 



chamber, the spermatozoa being 

 s\7ept in with the respiratory 

 current, and coming' in contact 

 with the eggs as they are dis- 

 charged. 



An excellent general Yiew of 

 the 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. 155, D) in alco- 

 hol, and then making trans- 

 verse sections. A section can 

 be floated off in water and ex- 

 amined with a lens. The per- 

 fect bilateral symmetry of parts 

 will thus be seen. 

 The above description will answer for the majority o± la- 



Fig. 160. — Pedal ganglia and oto- 

 cyetB (earn) of the clam, magnified 10 

 diameters. ^, pedal ganglia; e, pedal 

 commissures:/, line of union of gan- 

 glia ; g^ nerve from commissure to 

 muscles of foot ; ft, auditory nerve ; i, 

 otocyst ; k, nerves from ganglia to 

 tlie pedal muscles.— Drawn oy W. K, 

 Brooks, 



Ilg. 161.— Umffl ftfOT??, flylne through the water, its long nnmerons fllaments ex- 

 tended.— From Brehm's ■' Thierieben." 



iiaellibran,chiate nj^oUusks ; in the oyster (Ostrea) or iij Ano- 



