The Central Nervous System of the 

 Pycnogonid Lecythorhynchus 



WILLIAM A. HILTON 



During tlie summer of 1914 the pycnogonid Lecythorhynchus 

 marginatus Cole was found abundantly at Laguna Beach and the 

 results of a general study of the central nervous system are 

 given at this time. 



The small size of the animals made sectioning methods neces- 

 sary from the start. Because of the hard exoskeleton, great 

 difficulty was experienced in preparing slides, and a number of 

 specimens were cut before complete series were obtained. 

 Nothing in the fixation seemed to greatly help, but certain 

 individuals seemed to have softer cuticle. 



There are six chief ganglia forming the central nervous 

 sj'stem of the adult. The more cephalic centers are a little 

 smaller than the others. 



Five ganglia are described by Dohrn '81 and others, due no 

 doubt to a more definite fusion of certain centers. In the 

 embryo of Palene, as described by Morgan '91, there are 

 ganglia corresponding to each of the pairs of appendages, 

 those of the seventh or last ]>air and the abdominal ganglia 

 appear last in development. 



Merton '07 describes six pairs of ganglia in Nymphon 

 parasiticum, the second pair, or the first subesophageal center, 

 is clearly shown to be composed of two parts on each side, but 

 the last pair represents the abdominal ganglia, if one may 

 judge from the figure given. 



In L. marginatus the first three cephalic ganglia are quite 

 close to each other and partly fused, as the figure shows. The 

 last three ganglia are more widely separated. From one to 

 two abdominal ganglia are described in other pycnogonids. In 

 this species the abdomen is very small and no ganglia were 

 found. Probably all of the abdominal elements are fused with 

 the last thoracic ganglion. 



