172 GENERAL CONSIOERATION.S. 



to the lateral by means of one or more enlarged connectives; and in a few species 

 a postei'ior commissure may complete a circumrectal ring. In the Neomeniina 

 fibres fi'om the dorso-posterior enlargements have been traced into the tissue 

 surrounding the shell gland, into the body wall and in Sirophomenia ophidiana 

 delicate nerves have been traced from the enlargements of the lateral ganglia 

 into the heart. In the Chaetodermatidae practically all of the nerves inner- 

 vating the posterior end of the body spring from the suprarectal commissure 

 or in close proximity to it. In Limifossor the gills are innervated by two pairs 

 of branches from the commissure and in Chactodcnna aUenuata, C. erudita and 

 probably others the same is true. I have been unable to find a circumrectal 

 ring described by Wiren ('92). 



The labio-buccal system has been examined critically in a few species only, 

 yet the few facts gleaned indicate that in a typical condition it is not unlike what 

 is found in the Chitons. For many years the so-called buccal ring has been 

 known both in the Chaetodermatina and in the Neomeniina, consisting of two 

 connectives coursing along the sides of the pharynx and uniting with two ganglia 

 in the neighborhood of the radula or the outlet of the ventral salivary glands. 

 These ganglia, which I have termed labio-buccal, are in turn connected by means 

 of a ventral commissure, which in the genus Chaetoderma bears two small 

 ganglia. In Proneomenia hawaiiensis there is a very* distinct subradular organ, 

 consisting of two clearly defined circular patches of high epithelial cells on each 

 side of the mid line in front of the radula. In close proximity to these are small 

 ganglia, united by a commissure, and on the other hand joined with the labio- 

 buccal ganglia by connectives. In addition there is a dorsal commissure uniting 

 the labio-buccal connectives and possibly another ventral one. These same 

 elements in a more compact form, exist in Strophomenia scandens. In the genus 

 Chaetoderma I have recently shown that in front of the radula connectives 

 attached to the labio-buccal connectives, and, after giving off nerves which pass 

 directly to modified epithelial patch in the pharynx, are united with a single 

 ganglionic mass. In Limifossor there is in addition to the well-known commis- 

 sure a dorsal one and probably a second ventral one. In Dorijmenia acuta there 

 are two dorsal commissures and two ventral, one of which bears a pair of small 

 ganglia. The radula is certainly in a degenerate condition in several species 

 of Solenogastres ; it has disappeared in others and the same extremes exist in 

 the case of the subradular organ. Consequently it is not remarkable that the 

 system of ganglia and nerves associated with these sensorj' areas exhibit marked 

 differences in the various species. 



