OF THE CLAM. 



227 



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 the eggs as they are dis- 

 charged. 



An excellent general view 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 



Fig. 160. Pedal ganglia and oto- 

 cysts (ears) of the clam, magnified 10 

 diameters, d, pedal ganglia; e, pdal 

 commissures;/, line of union of gan- v. p flnatprl off in wnt.pr and PX- 

 glia ; g, nerve from commissure to 



muscles of foot ; A, auditory nerve ; i, amilied With a leilS. The per- 

 otocyst ; k, nerves Jrom ganglia jtp A 



feet bilateral symmetry ot parts 

 will thus be seen. 

 The above description will answer for the majority 01 la- 



the pedal muscles. Drawn by W 

 Brooks. 



Fig. 161. Lima hlans, flying through the water, its long numerous filaments ex- 

 tended. From Brehm's "Thierleben." 



mellibranchiate mollusks ; in the oyster ( Ostrea) or in A no- 



