254 i{. I. pococK. 



if there are any who see in it the homologue of the 

 Scorpion^s entosternite, tliey will renienil)cr tliat cliitin has 

 been shown (Lankester, p. G) to be present in the ento- 

 sternites of Scorpio, Mygale, and Limnlns, and will realise 

 the possibility of the formation of the rigid and horny 

 Galeodean entosternite by increased development of its 

 chitin, followed or accompanied by fnsion with the exo- 

 skeleton of the second post-oral somite. 



Briefly, then, of the three suppositions that may be enter- 

 tained with res^ard to the "entosternite" of the Solifnofa*. 

 each points to its being' a specialised, not a ]niniitive 

 structure. (1) If it is an en to scler i te, as Bernard and 

 Schimkewitsch maintain, it is not the homologue of the 

 entosternite of other Arachnids, which is shown by its 

 morpholog-y and development to be an entochondrite, pro- 

 duced by the condensation of connective tissue and the fusion 

 of muscular fibres and tendons. In this case it has func- 

 tionally replaced the true entosternite, and is a lecent 

 specialisation, not a primitive structure. (2) If it is an 

 endochondrite and the homologue of the entosternite of other 

 Arachnids, its structural similarity to, and fusion with, the 

 exoskeleton also attest high specialisation, (o) If it has 

 resulted from the union of the true entosternite with a pair 

 of exoskeletal ingrowths — if, say, the expanded portion 

 snppoi'ting' the alimentary canal coi-responds with the true 

 entosternite, and the pillars diverging- therefrom to the exo- 

 skeletal elements, — the absence of all trace of union between 

 the two, the complete continuity of their tissues, again 

 indicate great specialisation, 



'J'he evidence in favour of the truth of the first supposition 

 is almost strong enough to enforce its unquestioned accept- 

 ance. But whichever of the throe prove consonant with fact 

 and be ultimately adopted, the SolifugiX3 must be regarded 

 as the most specialised typo of Arachnid known, so far as the 

 oi'gau under discussion is concerned — a conclusion which is 

 perfectly in accord with man_y, nay most, of the structural 

 features of this order. 



