228 R. I. PorocK. 



a median process which divides into a pair of diverging 

 tendinous apophyses. From tlie sides of the neural ring 

 externally spring muscle-supporting processes. The muscles 

 rising from the posterior of these processes are extended 

 laterally and dorsally to become attached to the sides and 

 roof of the body-cavity, forming, with iissociated connective 

 tissue, a great muscular sheet or " diaphragm " which sepa- 

 rates the cavity of the prosoma from that of the mesosoma. 

 Inferiorly this partition is completed by muscles which run 

 from the posterior side of the lower edge of the neural canal 

 to the floor of the body-cavity. In the middle line above the 

 "body" of the entosternite the connective tissue of this 

 muscular sheet is perforated by two foramina ; the inferior 

 gives passage to the alimentary caual, the su})erior Lo the 

 aorta. 



In addition to the muscles already mentioned, three pairs 

 of dorso-ventral muscles arise from the entosternite. Those 

 of the posterior pair are attached to the underside of the 

 tergite of the genital somite behind the diaphragm, and to 

 the posterior side of the entosternite in front of it. Hence 

 in their passage from above downwards they pass through 

 the diaphragm. The median pair extends from the aortic 

 foramen in front of the diaphragm to the posterior border 

 of the upper surface of the "body" of the entosternite. 

 Just in front of their inferior points of attachment spring 

 those of the anterior pair, which, rising vertically, meet in 

 the middle line above the aorta, before attaching themselves 

 to the underside of the carapace. 



As might be expected, the entosternite of this sj)ecies 

 agrees in all essentials with that of Pal am u a; us indus 

 (=Buthus cyaneus) as described and figured by Lankester 

 (6) and lieck (1). In a general way the entosternite of all 

 Scorpions is formed on this plan. In minor particulars, 

 however, there is considerable structural variation. In 

 species with the metasternite antero-posteriorly compressed, 

 the body of the " entosternite " becomes shorter as con)pared 

 with its length, as shown in the ligure of that of lurus 



