NERVOVS SYSTEM OF SCORPION. 



am 



several papers, the last of which (1887) contains the results of 

 all his work on the subject. He worked out the nerve cell- 

 groups and the nerve fiber-tracts 

 and came to the conclusion that 

 there are two pre-cheliceral neu- 

 romeres in the scorpion. But 

 his observations do not seem to 

 support his conclusions, for, while 

 he showed that there are, cor- 

 responding to these two neuro- 

 meres, two pairs of optic lobes, 

 he described their nerve-fiber 

 tracts communicating with the 

 interior of the "brain" as united 

 to form one. He showed great 

 complexity in the structure of 

 the " brain." 



In 1890, Patten, in a prelim- 

 inary paper on the origin of ver- 

 tebrates from arachnids, com- 

 pared the arachnid cephalothor- 

 acic nerve mass, or "brain," 

 with the vertebrate brain, turn- 

 ing the former up-side-down in 

 order to get the proper relation 

 with the digestive tube. In the 

 scorpion embryo he found three 

 precheliceral neuromeres, each 

 with a pair of optic ganglia. In 

 each optic ganglion was an in- 

 vagination. The cephalo-thor- 

 acic nerve mass was composed 

 of thirteen neuromeres. In the 

 adult, a typical neuromere had a 

 pair of " neural " nerves and two 



FIG. 3. Third stage of same, X 45- On one side the head is represented as an 

 opaque object, a, anus ; a& 1 , first abdominal appendage ; ec, anterior margin of the 

 ectoderm growing over the first neuromere ; n 20 , twentieth neuromere ; ol, ectodermal 

 thickening to form the lateral eye ; om, ectodermal invagination to form the median 

 eye sac ; s/, semilunar lobe ; r, rostrum. 





