ALFRED C. HA.DUON. 



in Mnrex erinaceus. Fig. 15 shows the proliferation [pg) which 

 forms a pedal ganglion. Close by it is seen the newly-formed 

 otocyst {ot). The sense organs are developed by involution from 

 the same tissue (see figs. 16 and 17). 



These statements differ most materially from those of Bo- 

 bretzky,^ who " plodded at section- cutting to elucidate the 

 question as to the origin of the nerve elements/' and who arrived 

 at the conclusion '^ that (in Fnsus) the ganglia arise as a massing 

 together of mesoderm cells " (p. 143) , I would venture to 

 suggest that we may regard his account as either depending upon 

 the occurrence in Fusios of "precocious segregation" (Lankester), 

 as is apparently the case in the Cephalopoda, or, more probably, 

 arising from an error of observation on the part of this accurate 

 and painstaking observer ; for it seems to be very unlikely that 

 Fnsus should differ so much in the development of these im- 

 portant organs from the allied genera Purpiira and Mnrex. 



According to Fol,^ in Limax, the pedal ganglia arise from the 

 mesoblast of the foot, while the supra- oesophageal ganglia are 

 developed from the epiblast of the velum ; this manifestly re- 

 quires corroboration. 



Accepting these conclusions then, the Cephalopoda appear 

 to be unique in having a mesoblastic nervous system — a point 

 which requires to be again worked over. 



1 N. Bobretzky, 'Arch. f. Mik. Anat./ xiii, 187G. 



2 H. Fol, 'Compt. Rend.,' 1875, p. 523-G. 



