COMPARATIVE ANATOMY. 35 



and hence a perfect individuality, until they pass into the brain. In some ofher 

 species of the genus, as for example Chaetoderma nitidulum, they fuse indistin- 

 guishably as they enter the brain. Finally in Limifossor the pedal and lateral 

 cords fuse a comparatively long distance from the brain, and at a less remote 

 position are completely united with the labio-buccal connective. 



In every case the pedal ganglia are almost as long as the animal and hold 

 a ventral position on each side of the pedal furrow though not always in close 

 proximity to it. In several species commissures at fairly regular intervals have 

 been seen uniting these cords, and equally numerous connectives have been 

 traced to the lateral nerves which hold a more dorsal position along the sides of 

 the body. In the posterior end of the animal the relation of these elements varies 

 considerably in the different species. In Proneomenia hawaiiensis, for example, 

 the pedal cords become reduced in calibre, and finally break up into small nerves 

 which have not been shown to have any connection with the lateral cords though 

 they come into the neighborhood of some of the small nerves originating from 

 them. In Strophomenia scandens the last two or three latero-pedal connectives 

 are of relatively large size and the union of the lateral and pedal ganglia is clearly 

 established. Furthermore in several species, such as Lepidometiia hystrix, and 

 Neomenia carinata, the posterior ends of the pedal cords terminate in ganglionic 

 enlargements (ganglion posterius inferius, Wiren) united by a commissure of 

 more than usual size situated ventral to the rectum. The posterior ends of the 

 lateral ganglia are also frequently enlarged (ganglion posterius superius) and are 

 invariably united above the rectum, thus completing in several species a circum- 

 rectal nerve ring. In the Chaetodermatidae the lateral and pedal ganglia are 

 united, at least in the anterior end of the body, by commissures and connectives 

 but more posteriorly these main ganglionic cords terminate in a large nerve mass, 

 the so-called gill ganglion, continuous across the mid line above the rectum. 



In what probably rejiresents a typical condition the sublingual or buccal 

 system, in reality the labio-buccal, holds essentially the same relations as in the 

 Chitons. Connectives lead from the brain along the pharyngeal wall and unite 

 with ganglia about opposite the forward end of the radula or in the neighborhood 

 of the openings of the ventral salivary glands. These nerve masses probably 

 represent the labial and buccal ganglia of other molluscs, and in at least one 

 species, Strophomenia scandens, are united by three commissures and the sub- 

 radular system. One of these commissures, the dorsal buccal, crosses the dorsal 

 side of the pharynx, while two pass ventral to it. In Proneomenia hawaiiensis, 

 where the subradular system is most highly developed, a connective arises from 



