STUDIES ON THE ARACHNID ENTOSTERNITE. 253 



regard the ventral processes ns the representatives of the 

 ventral moieties of these same muscles ? 



Bernard's hypothesis involves the assumption of a degree 

 of dislocation and rearrangement of nuisclos and integu- 

 mental apophyses for which it is difficult to find justification. 

 I can discover no evidence that the sternal scars of the 

 Mygalomorphse and the ventral processes of the entosternite 

 which rise from them are the remains of integumental dis- 

 sepiments. If this were the case wo should expect to find an 

 intimate unseverable union between the sternum and the pro- 

 cesses in question. No such union exists. The expanded ex- 

 tremities of the processes may be readily detached, the extent 

 of their union with the sternum being quite compatible with 

 the theory of their muscular origin, but hardly reconcil- 

 able with that of their derivation from ectodermic ingrowths. 



The basis of Bernard's hypothesis is to be found, firstly, 

 in the structure and relations of tlie so-called entosternite of 

 the Solifugfe, which is shown by its histology and union 

 with the integument to be an ectodermic entapophysis ; 

 secondly, in the assumption that this skeletal piece is the 

 morphological equivalent of the entosternites of other 

 Arachnids; thirdly, in the conception that the Solifugas 

 I'etain a more archaic type of prosoma than that of the other 

 orders of this class. 



Assuming the truth of the propositions here stated or 

 implied, the conclusion Bernard draws as to the ectodermic 

 origin of the entosternite in the Spiders, etc., necessarily 

 follows. But from what is known of the structure and 

 development of the entosternite in the two orders there is 

 little doubt that the first proposition is true, and that the 

 second is untrue. As for the third, it is a matter of opinion 

 depending upon the standpoint from which the morphology 

 of the Arachnida is regarded. 



The available evidence is, in my opinion, decidedly in 

 favour of the view that the "entosternite" of the Solifuga) 

 must be regarded as a post-oral ontosclerito comparable to 

 the crescentic pre-oral entosclerite of the Scorpions. But 



