466 WILLIAM A. HILTON 



some others have used gross dissection with the larger species. 

 I also tried this method and found that it was not difficult to 

 expose and remove the whole nervous system from even the 

 smallest specimens. For the structure of the ganglia serial 

 sections were made from these removed ganglia. 



There seems to be some difference of opinion as to number 

 and position of abdominal ganglia. There are without doubt 

 ganglia in the adult that may be called abdominal, but they are 

 often not evident or indicated by slight knobs on the last gan- 

 glion. Probably in no case are these little ganglia in the abdo- 

 men (figs. 1, 2, 6, 7, 19). 



The special nerve supply to the proboscis has been described 

 by Hoek, Dohrn and others. I was able to dissect it out in a 

 number of species where I have found essentially the same 

 features already described. In the genus Pycnogonum I found 

 a similar condition as shown by Hoek. Practically the same 

 condition was found in two other genera not before described. 

 There are three main branches which run to the three divisions 

 of the proboscis: a dorsal branch running from the mid-ventral 

 line of the supraesophageal ganglion, and two lateral branches 

 springing from the forward part of the first ventral ganglion. 

 Each of these branches has numerous small ganglia along its 

 course and near the end of each branch there is a much larger 

 ganglion. Branches connect the three trunks with each other 

 and fine nerves run from each ganglion to adjacent parts of 

 the proboscis. Lateral to these three ganglionated branches 

 is a more external nerve which sometimes has a separate ori- 

 gin from the larger ganglia or from the ganglionated trunks. 

 These three more superficial branches appear to fuse in places 

 with the deeper branches, but they do not bear ganglia. 



This whole complicated structure seems quite unusual and 

 some have seen in this proboscis region the I'epresentations of 

 other segments of the animals. However I prefer the assump- 

 tion of Dohrn that the proboscis represents only a secondary 

 growth of the lips of the stomodoeum. I believe the special 

 nerves of the proboscis represent the system of frontal nerves 

 and ganglia which we find in Insecta and other arthropods. 



