168 



THE FRESH-WATER MUSSEL 



[CH. VI 



.16 



artificial conditions of an 

 aquarium the animal, in my 

 experience, never buries itself 

 so deeply. The easiest me- 

 thod of securing specimens 

 from situations out of arm's 

 reach is to cut a long stick 

 to a fine point and carefully 

 insert the pointed end into 

 the inhalant siphon ; the 

 animal immediately closes 

 the valves of the shell, and 

 with such firm pressure that 

 it clings to the improvised 

 fishing-rod, and may be 

 bodily withdrawn from the 

 water. This method, which 

 is simple enough as soon as 



the eye has become accus- Fig..30 Dorsal view of 



J mutabihs, with the upper wall 



10 



tomed to the refraction due 

 to the surface of the water, 



stirring up the mud, so that 

 the water remains clear and 

 other specimens are ob- 

 tainable at the same spot. 

 The movements of the 



of the pericardium removed to 

 show the heart x about 1. After 

 Hatschek and Cori. 



has the advantage of not 1. Foot. 2. Anterior adductor 



muscle. 3. Retractor muscle. 



4. Anterior protractor muscle. 



5. Posterior protractor muscle. 



6. Posterior adductor muscle. 



7. Dorsal siphon. 8. Ventral 

 siphon. 9. Anus. 10. Split 

 between left and right mantle 

 lobes through which larvae may 

 leave the epibranchial chamber. 



11. Keber's organ. 12. Rectum 

 traversing ventricle. 13. Nephrostome or internal opening of organ 



of Bojanus. 14. Ventricle. 15. Left auricle. 16. Anterior 



protractor muscle. 

 [The muscles are named in accordance with their respective functions.] 



