88 PRONEOMENIA HAWAIIENSIS. 



backward to unite with the pedal gangHa that occupy the usual ventral positit)n; 

 while the labio-buccal connectives pass backward along the sides of the pharynx 

 and unite with the labio-buccal ganglia that are placed at the sides of the radula. 

 About mid way between the brain and ganglia the labio-buccal connectives are 

 united by a commissure (dorsal buccal) that passes across the dorsal side of 

 the pharyngeal wall, while a second (ventral buccal) passing over the radula 

 unites the buccal ganglia. Each of these last named nerve masses, connected 

 by the well-known commissure dorsal to the radular sac, gives rise to a prominent 

 nerve that passes inward and unites with a ganglion situated near the base each 

 of the subradular organs mentioned in connection with the radula. Each sub- 

 radular ganglion is in turn connected with a commissure imbedded in the tissue 

 beneath the pharynx. The relations of these ganglia and the attendant sense 

 organs is essentially the same as in the Polyplacophora. They are much more 

 concentrated in the latter group but the various elements may be readily 

 homologized. 



Through the body proper the pedal and lateral cords are united by con- 

 nectives corresponding roughly to the number of gut pouches. About the same 

 number of commissures also unite the pedal cords. These connectives and 

 commissures disappear about the middle of the slimo gland and a short distance 

 beyond this point the pedal cords disappear apparently without forming a 

 posterior connective (Plate 13, fig. 4). The lateral cords on the other hand pass 

 into the posterior ganglia that give rise to many nerves supplying the surround- 

 ing tissues and are united by a strong commissure dorsal to the intestine. In 

 the mid line this commissure develops a nerve that supplies the dorsal sense 

 organ. 



The dorsal sense organ is located on the mid dorsal line a short distance from 

 the hind end of the animal. Sections show that the cuticle in this region is 

 almost wholly lacking and that the neighboring spines bend over and protect 

 the otherwise naked sensory area. In each specimen the spines were much 

 worn and the upper part of the sensory hollow was filled with debris so that no 

 outward sign of this organ was visible. In one individual, probably abnormal 

 in this regard, there were two dorsal sense organs, one a short distance in front 

 of the other in the mid line. The posterior one corresponds most closely to 

 the single one of the other individuals and will be first described. 



The cuticle over the sensory region is almost wholly absent and the hypo- 

 dermal cells, that ordinarily are small and distinct, become clearly defined, 

 columnar, and depressed below the general level of the hypodermis. To the 



