8. The fact that the eye and hand need such guides shows how untrustworthy the senses are. A similar argument occurs in _Luc._ 86. _Perpendiculum_ is a plumb line, _norma_ a mason's square, the word being probably a corruption of the Greek γνωμων (Curt. _Grundz_ p. 169, ed. 3), _regula_, a rule. 9. The different colours which the same persons show in different conditions, when young and when old, when sick and when healthy, when sober and when drunken, are brought forward to prove how little of permanence there is even in the least fleeting of the objects of sense. 10. _Urinari_ is to dive; for the derivation see Curt. _Grundz_ p. 326. A diver would be in exactly the position of the fish noticed in _Luc._ 81, which are unable to see that which lies immediately above them and so illustrate the narrow limits of the power of vision. 11. Evidently an attempt to prove the sense of smell untrustworthy. Different people pass different judgments on one and the same odour. The student will observe that the above extracts formed part of an argument intended to show the deceptive character of the senses. To these should probably be added fragm. 32. Fr. 19 shows that the impossibility of distinguishing eggs one from another, which had been brought forward in the _Catulus_, was allowed to stand in the second edition, other difficulties of the kind, such as those connected with the bent oar, the pigeon's neck, the twins, the impressions of seals (_Luc._ 19, 54), would also appear in both editions. The result of these assaults on the senses must have been summed up in the phrase _cuncta dubitanda esse_ which Augustine quotes from the _Academica Posteriora_ (see fragm. 36). BOOK III. 12. This forms part of Varro's answer to Cicero, which corresponded in substance to Lucullus' speech in the _Academica Priora_ The drift of this extract was most likely this: just as there is a limit beyond which the battle against criminals cannot be maintained, so after a certain point we must cease to fight against perverse sceptics and let them take their own way. See another view in Krische, p. 62.