One can assert, with far greater right, that a sufficient ground for squint is not given by slight degrees of hypermetropia, for the latter are accommodatively overcome and binocular fixation retained by youthful persons without any difficulty, even when the additional motives enumerated by Donders are present. I have endeavoured to obtain a foundation for the depreciating influence of these circumstances favorable to squint, for I counted in my private practice, at the same time with the cases of squint, those cases also in which, despite those conditions which lessen the value of binocular vision, squinting was not present. Taking notice then of those cases in which the hypermetropia of the better or less hypermetropic eye amounted to at least 1·5 D., in order to allow the influence of the hypermetropia to be more conspicuous. The patients from which the above-cited 219 cases of convergent strabismus with a hypermetropia of at least 1·5 D. are drawn, comprised also 117 cases in which, with the same degree of hypermetropia and simultaneous difference of refraction or monocular amblyopia, no convergent squint was present; of these cases 101 had acuity of vision to 1/7; less than 1/7 to V. = 1/12 7, and V. less than 1/12 to V. 1/36 9 cases. The percentage 219: 117 = 100: 53, which is yielded for the middle and higher degrees of hypermetropia, is not exactly convincing for the accommodative theory of squint; it would be placed still less favorably if we were to include the lowest degrees of hypermetropia in the statistics. In face of these facts I do not consider it a happy question, that of seeking after "reasons for the prevention of squint." We do not want to quarrel with Donders over the question why all hypermetropes do not squint. Here, of course, I quite agree with Ulrich that squint does not occur if the necessary muscular conditions are absent. The identity of the fields of vision, on the other hand, seems to me to be of no importance for the age at which squint usually commences. This identity presupposes the habit of binocular fusion; but convergent squint arises, as a rule, before this habit is acquired. But even if binocular fusion were already learnt, it is given up with astonishing rapidity by children as soon as squint develops itself (see Case 16). The fixed habit of binocular fusion and the identity of the fields of vision dependent on it, is contracted only when squint does not occur, notwithstanding the presence of conditions favorable to it. However, the number of cases is so considerable in which, despite the presence of the causative motives suggested by Donders, no convergent strabismus is present, that the co-operation of other causes is necessary for the production of squint, and the first thing we do is to think of those causes which lead to squint even without hypermetropia.