CIRCULATORY SYSTEM IN ARACHNIDA 



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7. The genital opening is on the second abdominal somite. 



8. The first caudal segment in scorpions is not a true somite, 

 but merely the anterior division of the fourteenth postoral somite. 



9. If the number of preoral somites in Arachnida is not more 

 than four, as represented by the median ocular, lateral ocular, 

 rostral, and cheliceral somites, then the total number of somites 

 in Arachnida is twenty-one. 



EXPLANATION OF PLATES 



ABBREVIATIONS 



AC, Cheliceral artery 



AO, Aorta 



AP, Pedal artery 



APP, Pedipalpal artery 



1. AT, First abdominal tergite 



AV, Anterior aortic valve 



BR, Brain 



CA, Comb-artery (ninth vertical ar- 

 tery) 



Cbp, Basal plate of comb 



CO, Aortic arch connection with 

 thoracic sinus 



D, Diaphragm 



DP, Dilator muscle of the pharynx 



DS, Dorsoventral muscle separating 

 the first cephalothoracic diverticle 

 of the midgut from the second 



GB. 2, Gnathobase of the second leg 



GP, Genital- plate (operculum) 



H, Heart 



LC, Longitudinal connective between 



the fourth and fifth abdominal 



ganglia 

 M, Mouth 



MA, Anterior edge of carapace 

 ME, Median eyes 

 MG, Midgut 



MP, Posterior edge of carapace 

 PH, Pharynx 



SAA, Supraneural (epineural) artery 

 SBA, Subneural (hyponeural) artery 

 ST, Sternum 

 UP, Upper lip (rostrum) 

 VA, Vertical or interneural artery 



