JiN^TOMT OF THE CLAM. 



227 



gills, where the embryos in some species partially derelop. 

 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- 

 Fig. 160. -Pedal ganglia ^nd pt<v 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 oi la- 



cysts (ears) of the clam, magnitied 10 

 diameters. e2, pedal ganglia; e, p"dal 

 conunissures;/, line of union of gan- 

 glia ; g, nerve from commissure to 

 mnscles of foot ; A, auditory nerve : i, 

 otocyst ; A, nerves from ganglia to 

 the pedal muscles.— Drawn TjyW E. 

 Brcink?. 



Jig. 161.— Mmu hlans, flying through the water, its long nnmerons filaments ex- 

 tended. —prom Brehm's " Thlerleben." 



mellibranchiate moUusks ; in the oyster {Ostrea) or in Ano- 



