188 Thirty-fifth Keport ok the State Museum. 



pal nerves, there are other small nerve filaments supplying the differ- 

 ent organs of that portion of the animal with nerves. 



The auditory organ consists of a sac attached to one of the 

 branches of the nerve proceeding from the lower end of the pedal 

 ganglion, is filled with colorless fluid, and contains a hard body called 

 the otolith, which is covered with cilia and keeps up a constant 

 rotary motion. 



The sense of touch appears to be very acute, more especially in 

 the foot proper ; the slightest touch, when the foot is expanded, causing- 

 it to contract immediately. 



Though possessed of an organ of hearing and without organs of 

 sight, as far as our present knowledge extends, the Anodonta is much 

 more sensitive to light than to sound. I have kept a large number in 

 a tank for several months, and have thus had a good opportunity to 

 judge of the effects of sound and light, and from the observations and 

 experiments I have made, it seems certain that they are not affected by 

 any sound which does not communicate a visible jar to the water. 



That they are sensitive to light is shown by the fact that on bright 

 days the rudimentary siphons are more fully expanded, and the inha- 

 lant and exhalant currents much stronger than on cloudy days or at 

 night ; at which times the shell is generally closed. 



The use of the tentacles surrounding the inhalent siphon has not 

 been satisfactorily determined. It is possible that they will prove to 

 be organs of sight. It seems impossible that animals so sensitive to 

 light should be without special organs of vision. 



Circulatory System. 



The blood of the Anodonta is colorless. The corpuscles are simi- 

 lar in form and structure to colorless blood corpuscles of man, and 

 have the same continually changing movements. Owing to the 

 soft jelly-like nature of the animal substance, it is extremely difficult 

 to determine with accuracy many points in relation to the circulation. 



From the ventricle of the heart proceed two aortse (from the Greek 

 word aoprv[ the heart), a name applied only to the arteries which pro- 

 ceed directly from the heart. The anterior aorta (PI. 10, a. ao. ) enters 

 the body above and in close contiguity to the intestinal canal, bending 

 slightly to the right, turning downward and a little posteriorly, one 

 branch entering the mantle : just behind the anterior adductor 

 muscle a large branch goes downward and runs parallel with the mar- 

 gin of the foot, between the muscular portion of the foot and the body 

 proper, sending numerous branches down to the ventral margin of the 

 foot. Immediately after this branch leaves the main artery it sends out 

 a branch to the anterior adductor muscle, mouth, and other anterior 



