Mr. Garner on the Nervous System of MoUuscom Animals. 493 



in this little animal eleven ganglia. The genus Trochus appears similar in 

 its nervous system, as docs Cijclostoma* . 



In Neritina (fig. 10& 11.) we find the two branchial and pedal ganglia of 

 Patella become quite united into a transverse oval mass (O.), which, there- 

 fore, as well as the foot, also supplies the nerves we have just seen going from 

 the superior compound ganglia. The two connecting filaments remain di- 

 stinct as they were in Patella. 



The Planorbis (Tab. XXVI. fig. 7 & 8.) has a nervous system rather remark- 

 able, as the animal itself is in other respects, being organized to respire both 

 air and water. There is a branchial cavity with a wide anterior opening as 

 usual, containing a long branchial appendage ; a small opening leads out of 

 this cavity into the pulmonary cavity. Near this opening is the rudiment 

 of the other branchial appendage. Two filaments connect the separate 

 lateral superior ganglia (A.) with the inferior part of the ring, where the four 

 ganglia with their connecting nerves form a quadrangle. The branchial 

 cavity would appear to be supplied from the two posterior ganglia of these. 

 A filament from the right side mounts over the oesophagus, joining one from 

 the left, and together they form a ganglion supplying the pulmonary cavity 

 situated to the left. Some filaments (e.) likewise from the posterior part 

 of the quadrangle and from the ganglion just described, supply the shell- 

 muscles, and form a small ganglion (G.), supplying the branchial appendage 

 and viscera. 



In Carocolla (Tab. XXV. fig. 12.), Helix, Umax, Partula, Achatina, an<i 

 Bulimus (fig. 13.) the author finds little difference in the form of the nervous 

 system. The brain when cut across over the oesophagus appears of a diamond 

 form, a branch of the aorta dividing the anterior pedal portion below from the 

 posterior part. From the anterior part below arise the numerous nerves of 

 the foot {d.), others for the shell-muscles, and a few (/>.) for the flanks of the 

 animal : from the posterior portion in the centre proceed the visceral nerves 

 (/.), often forming a sympathetic ganglion (G.) on the stomach, and some- 

 times another in the right side, vviiich appears rather to belong to the genera- 

 tive organs than to the mantle : the posterior portion also gives origin, a little 

 without the last, to the nerves of the mantle, which here do not cross. The 



* Berkeley, Zool. Journ. 



