Anatomy of some Scorpi'otis. 187 



in a ventral direction from each ganglion. I have not found 

 this nerve in any of the forms I have dissected, and it seems 

 to me probable that previous observers have been misled by a 

 blood-vessel which passes ventrally between the two cords 

 close to each ganglion from the longitudinal vessel overlying 

 the nerve-cord. It is not easy to separate this vessel from 

 the ganglion, but microscopic examination makes its nature 

 evident. 



The most important part of the nerve-cord is that lying in 

 the mesosomatic and first metasomatic segments. Three pairs 

 of ganglia are present on this portion, and, according to 

 Lankester, their arrangement differs markedly in different 

 forms. In Androctonus [Prionurus) fanestas'^, Androctonus 

 occitanus f , Androctonus americanus |, and Androctonus hotten- 

 totus § the first two of these ganglia supply respectively the 

 third and fourth pairs of lung-books (eleventh and twelfth 

 segments), the third ganglion supplying the first meta- 

 somatic segment. The segments anterior to the eleventh are 

 innervated from the prosomatic ganglion-mass. In Scorpio 

 italicus\\, Scorpio cyaneus^y JBrotheas subnitens ^*, and two 

 species of Telegonini ft, on the other hand, the first two 

 ganglia supply the second and third lung-books respectively, 

 while the fourth pair is supplied by the third ganglion. In 

 these, therefore, the prosomatic ganglion supplies only the 

 segments as far back as the first pair of lung-books (seg- 

 ment 9). 



In view of the great morphological importance of these 

 differences, I have devoted special attention to the point, and 

 have carefully dissected the nervous system in the following 

 forms: — Scorpio fulvipes, Opisthophthalmus capensis, Palam- 

 nceus ThoreUiij Opisthocentrus madagascariensisj Opistlto- 

 centrus vcdidus^ Hormurus australusice, Vejovis sp., Euscorpius 

 italicus, Broteochactas delicatus^ Bothriurus bonariensis, 

 Buthus nigrolineatuSy Parabuthus capensis^ Uroplectes trian- 

 gulifevj and Centrurus, sp. 



The conclusion I have arrived at is as follows : — The first 

 ganglion may vary in position between the level of the second 



* Prionurus hector (Koch). 



t Buthus europw.us (Linn.). 



X I'robably Centrui-us yracilis (Latr.). 



§ Parabuthus, sp. 



II Euscorpius italicus (Herbst). 



^ Scorjno megacephalus (Koch). 

 ** Teuthraustes atrame?darius (Sim.). 



tt C'araboctonus Keyserlingii (Poc), from Coquimbo, and Cercophoiiius 

 squavui (Gerv.), from Tasmania. For these synonyms I am indebted to 

 Mr. Pocock. 



13* 



