52 WILLIAM PATTEN. 



looked at without prejudice, is sufficient proof of the genetic 

 relation between the Arachnids and Vertebrates. It certainly 

 is not inferior to evidence based on the presence of a notochord 

 or gill-slits. However, this fact only furnishes the key-note 

 to the argument that is to follow. 



In adult Scorpions and Spiders the brain shows more 

 clearly its origin from three segments than is the case in 

 insects. In fig. 61 I give a diagrammatic view of the brain of 

 Arachnids based on my observations on Scorpions and Spiders. 

 None of the tegumentary nerves are represented, and, excepting 

 the position of the lateral ocelli, the diagram would do as 

 well for one as for the other. I was the first one to point 

 out the homology of the eyes of Spiders with those of 

 Scorpions and Insects in my paper on the ''Segmental Sense 

 Organs of Arthropods.'^ I stated, p. 601, '' In Spiders the 

 structure of the cephalic lobes is the same as that of Scorpions. 

 The two anterior median eyes belong to the second segment, 

 and are homologous with the median eyes of Scorpions, the 

 development being the same in both cases. The three 

 remaining pairs belong to the third segment, and are homo- 

 logous with the lateral eyes of Scorpions. They are invaginated 

 to form optic cups in the same way as those of Acilius." 

 Korschelt and Heider have overlooked this statement, for they 

 credit Kishinue and Purcell with having shown the similarity 

 in the development of the median eyes of Scorpions and the 

 anterior median eyes of Spiders, although their papers did not 

 appear until two or three years after mine. 



If further confirmation of this interesting fact is necessary, 

 it is found in the structure of the adult brain. In Scorpions 

 the optic ganglia of the second and third segments remain 

 distinct through life. They are carried by the movements of 

 the eyes on to the anterior face of the fore-brain, where they 

 remain as two pairs of conical projections, the anterior pair 

 united with the nerves to the median eyes (fig. 61). In the 

 brain of some Spiders, notably Epeira, according to St. Remy, 

 exactly the same condition prevails.^ But the anterior ganglia 



1 It must be remembered that the terms superior, anterior, and posterior, 



