LYMN.EID.E OF NORTH AMERICA. 15 



leaves the right visceral ganglion near the right pallial nerve, and 

 shortly joins a similar one from the abdominal ganglion, the combined 

 nerve passing to the vagina, the anterior part of the mantle and the 

 respiratory cavity. The left ganglion sends off a single long nerve 

 which innervates the mantle along its sides (20). 



The abdominal ganglion (4), which is really two ganglia fused 

 together, lies. behind and somewhat below the visceral ganglia, is con- 

 nected with the latter by two short, thick commissures, and sends off 

 four nerves. One of these has already been described under the right 

 visceral ganglion. The central nerve (23) is the longest and inner- 

 vates trie pericardium, aorta, part of the genitalia, the rectum, diges- 

 tive gland and respiratory cavity. A somewhat shorter nerve on the 

 right of this (22) furnishes nerve force to the posterior part of the 

 aorta and a part of the genitalia. To the left of the central nerve a 

 small nerve, arising apparently at a point between the abdominal and 

 left visceral ganglia, supplies the anterior part of the mantle (21). The 

 nerves of the abdominal and visceral ganglia also innervate different 

 portions of the digestive system. 



In a living specimen the ganglia are of a very bright orange color, 

 and in alcoholic specimens they are yellowish or yellowish white. The 

 eyes are as usual in androgynous Pulmonata. The sclerotic membrane, 

 choroid, cornea, etc., are well developed, and the optic nerve is very 

 large. 



In working out the foregoing Lacaze Duthiers' article in Archiv. 

 de Zool. Exp., has been followed as a guide. The nervous system of 

 the present species may be said to be almost identical with that of 

 Lymncea pcreger described and figured by Lacaze Duthiers (pi. 17, 

 fig. 2). Spengel's figure of Lymncea stagnalis is also the same (taf. 

 xvii, fig. 11), excepting that the nerves to the penis and vagina are 

 not shown. Moquin Tandon's figures are different, his Lymncea palus- 

 tris (pi. 34, fig. 27) showing a fused condition of the abdominal and 

 visceral ganglia. In his figure of Lymncea auricularia the pleural and 

 visceral ganglia appear to be fused and the nerves are insufficiently 

 shown. No figures, excepting those of Lacaze Duthiers', show the 

 innervation of the male and female genitalia. 



The special organs of sense in Lymnaea are those of touch, sight, 

 smell and hearing. The organs of touch are the flat, triangular ten- 

 tacles which may be repeatedly observed performing this function. 

 The organs of sight are the eyes which are well developed. Noth- 

 ing definite is known concerning the powers of sight in the fresh-water 

 pulmonates. Many Lymnaeas are known from experiment to love the 



