4 PATTEN AND REDENBAUGH. [Vol. XVI. 



cartilaginous body of varied form lying dorsal to the cephalic 

 ganglionic mass and ventral to the intestine. It functions as 

 a centrum for the attachment of various muscles. 



Schimkewitsch in '94 gave a very complete summary of all 

 the literature upon the subject. Therefore it will only be neces- 

 sary to call to mind those works which have an immediate 

 bearing upon the forms herein described. 



In '81 Lankester figured the plastrons of Linmlus, Mygale, 

 and Scorpio, and briefly compared them with each other in their 

 general characteristics. 



In '84 he gave a more complete account of the plastron of 

 Scorpio. He figured and described those of Apiis, Mygale, and 

 Limuhis, and gave something concerning the histology of all 

 four of them. 



In '85, with the aid of his pupils, Mr. Benham and Miss Beck, 

 he compared the plastrons of LimiUns and Scorpio with refer- 

 ence to their muscular attachments. 



In '89 Patten figured and described the plastron of a different 

 species of scorpion, and laid special stress upon the existence 

 of the subneural arch, or " occipital ring." His figure differed 

 from Lankester' s principally in the absence of a diaphragm. 



In '92, '93, and '94 came a series of papers by Schimkewitsch 

 and Bernard, in which Bernard sought to homologize the apo- 

 demes of Galeodes^'x'dx the endosternites of other arachnids, and 

 to show that the endosternites of arachnids are apodematous 

 structures due to fusion and compression of the cephalotho- 

 racic segments and later specialized for muscular attachments. 

 He regarded the endosternite of Limuhis as a derivation of the 

 ventral muscle bands and believed it to be homologous with that 

 of Apiis and not with that of arachnids. Schimkewitsch, on 

 the other hand, maintained that the apodemes of Galeodcs were 

 entirely represented by less developed apodemes in Scorpio, and 

 that the endosternite was a morphologically different structure. 

 He also stated that the arachnid endosternite was composed of 

 two parts: (i) of a transversal muscle corresponding to the 

 adductor muscle of Crustacea; and (2) of a pair, or perhaps 

 several pairs, of mesodermic tendons connected with the trans- 

 verse muscle strands. 



