STUDIES ON THE AKACHNID ENTOSTKRNITE. 241 



As explained below (p. 249), there are good reasons for sup- 

 posing that the four apophyses of constant occurrence in the 

 Araneas represent the tergal elements of the tergo-sternal 

 muscles of the second, third, fourth, and fifth somites of the 

 prosoma, those of the sixth somite being undeveloped as an 

 accompaniment of the compression this somite has suffered. 



Seeing how nearly related in many particulars the Aranoa? 

 are to the Pedipalpi, it can hardly be doubted that the four 

 apophyses in question iu the Aranete are homologous to the 

 four that project laterally iu the Thelyphonidte, the fifth 

 pair which is suppressed in the Spiders being retained in a 

 rudimentary state by the Pedipalpi. In the case of Phry nus 

 the question is complicated by the presence of an additional 

 apophysis on each side, making a total of five. The posterior 

 of these might be held to represent the apophysis which is 

 missing in the Arane^ and rudimentary iu Tliely jilionus ; 

 but since the last prosomatic somite in Phry nus is compressed 

 iu its sternal portion almost to the same extent as iu the 

 Aranea3, and since even iu 'J'helyphonus, where this somite 

 retains its more primitive condition, the apophysis is scarcely 

 developed, it seems more probable that this apophysis is also 

 undeveloped in Phry nus, and that the fifth apophysis iu 

 this genus actually corresponds to the fourth in the Spiders 

 and Thelyphonus. The likeliliood of the truth of this view 

 is enhanced by the basal juxtaposition of the third and fouith 

 apophyses in Ph ryuus, which forcibly suggests their common 

 origin from a tendon representing the third apophysis of the 

 Spiders and Thelyphonus secondarily subdivided into two. 

 The possibility of the subdivision of these apophyses is clearly 

 shown in the case of many Aranese, such as Ctenus and 

 Lycosa where they are deeply cleft, iu Acanthodon where 

 those of the third and fourth pairs are double down to the root, 

 and in Thelyphonus where the apophysis rising from the 

 upper side of the anterior coruu gives off a secondary branch 

 towards the middle line. 



Cleavage of primary single tendons may account for the 

 presence of the one or two pairs of supplementary teiuloiis 



VOL. 46, PAKT 2. MEW SEKIKS. ^ 



