71 



ClupeaPM and Pleiu-onectes limanda. Also with Gadidae tliis tract 

 can easily be traced from tlie siibveiitricular crossing as far as the 

 deep medullary layer of the tectum. 



Franz has erroneously indicated this bundle in Gadus, in fig. 6 

 of his work, as "ftbrae tect. n. opt." The correctness of my observ- 

 ation, however, can be tested not only in Gadus itself, but very 

 easily in Lota and Motella. In lig. 24 of the same work Fr.anz has 

 called the same tract correctly "ascending decuss. transversa" (the 

 upper line of his reference, at the bottom, left hand). 



Although I he exact way of origin and termination of this bundle 

 is not yet clear to me, 1 should like to call it provisionally tv. 

 tecto-prnerotuiidus and introduce it under this name. 



III. 7V. isthmo-praetectalis. 



Fk.\nz describes the course of his tr. istfn)io-Oj>i/.ciis as follows (op. 

 cil., p. 414): "a tract which, together wilh the opticus, first appears 

 ventrally to the midbrain roof, ascends on the inside of the midbrain 

 roof, reaches the torus semicircularis and here curves round to the 

 ganglion islhmi — here often difruMilt lo distinguish from tlie fibres 

 of the commissura transversa. It may be possible that part of the 

 fibres remains already in the torus semicircularis." 



He further is of opinion, supported by experiments (on which 

 fishes?) that the fibre tract arises undoubtedly from cells of the 

 ganglion isthmi and sends its nenriles centrifngally into the eye 

 (I.e., p. 415). 



My investigation confirms the presence of such a bundle and its 

 candal course, as described by Fr.AiNZ. I only want lo remark that 

 I could not find this bundle with all l>ony fishes. A few fishes. 

 such as Salmonids, Silnroids, Misgiirnus, Symbranchidae, E.sox, Ammo- 

 dytes?^), Gadidae, Lophius?') and Tetrodontidae? ') seem not to 

 [lossess such a fibre tract. 



Its further frontal course, however, is not as supposed by FraiNz, 

 but different according to the Teleosts examined. 



Fkanz seems to be right, in so far as the bundle, after its character- 

 istic curve in the torns senncircnlaris, gathers its fibres at the 

 lateral basal ridge of the midbrain, then by bnndles enters into 

 the lateral opticus root and disap|)ears from examination under the 

 fibi'es of the latter, as is the case with Megalops (with all)"), Gaslero- 



M The question-marks indicate here that the matter concerned is not quite clear 

 in these fishes. 



^) The brackets refer to the quantity of fibres, entering into the opticus root. 



