430 



SCIENCE. 



LN. S. Vol. V. No. 115. 



another by a loose mass of fibres running 

 parallel to the surfaces of the capsules. 



In the middle body this middle layer of 

 fibres is gathered into a bundle at the an- 

 terior margin of the body and passes out 

 towards the central portion of the brain. 

 Almost immediately the bundle divides. 

 One division goes to the calices of the mush- 

 room bodies, forming thus the antero-supe- 

 rior optic tract ; the other to the lower pos- 

 terior portion of the brain, forming the 

 antero- posterior optic tract. 



From the middle loose layer of fibres of 

 the inner body several bundles arise, all 

 penetrating the hinder portion of the brain. 

 One bundle forms an upper, another a lower 

 commissure between the two optic lobes. 



The fibrillar elements from the retina 

 terminate in five branches and thus help 

 to form the outer mass of fibrillar substance. 

 From cell bodies between the basement 

 membrane of the retina and this mass fibres 

 pass inward, give off short, fine fibrils 

 connecting with the terminating fibrils just 

 noted, and then go further inward, form- 

 ing, with their fellows, the outer chiasma 

 and terminate in a bunch of fibrils in the 

 outer capsule of the middle body. These 

 form neural elements 1. From cell bodies 

 between the outer chiasma and the middle 

 body fibres penetrate the outer capsule of 

 the latter, giving off a bunch of lateral 

 fibrils connecting with the terminals of ele- 

 ments No. 1. The main fibre then crosses 

 the body to the inner capsule, gives off in it 

 a group of short fibrils, then leaves the body, 

 and after forming, with their fellows, the 

 inner chiasma, finally terminate in the outer 

 capsule of the inner body of the lobe. 



From cell bodies between the margins of 

 the two bodies neural elements No. 3 arise, 

 that bear the same relations to the inner 

 body and its capsules as do elements No. 2 

 to the middle body. Passing out of the 

 concave surface of the inner body some of 

 the elements are gathered into a bundle that 



passes forward, forming the anterior optic 

 tract and terminate in the optic body, a 

 small oval mass of fibrillar substance above 

 the antennal lobe. Others go upward as a 

 bundle of fibres to the calices of the mush- 

 room bodies, forming thus the postero-su- 

 perior optic tract. 



The branching terminals of the fibres 

 forming the antero-superior optic tract seem 

 to connect with the lateral fibrils of element 

 No. 2 in the inner capsule of the middle 

 body, and the terminals of the fibres form- 

 ing the posterior optic tracts connect simi- 

 larly with the inner lateral fibrils of ele- 

 ments No. 3. 



A stimulus to a retinal element may reach 

 the central portion of the brain by passing 

 over three or four neural elements and may 

 reach either the mushroom bodies, the optic 

 body or several portions of the posterior 

 part of the brain, or passing over more ele- 

 ments it may reach all these regions, and 

 even be transferred overthe two optic com- 

 missures to the opposite lobe, and thus indi- 

 rectly reach the mushroom bodies, the optic 

 body or the posterior portion of the brain 

 on the other side. 



The earliest differentiation in the central nervous 

 system of Vertebrates. A. Schaper. 

 The speaker presented briefly some of the 

 results of his recent investigations on the 

 histogenesis of the central nervous system 

 which are to be published in extenso in the 

 ' Archiv fiir Entwicklungsmechanik.' The 

 essential points of this paper were the fol- 

 lowing : 



1. The so-called ' Keimzellen ' of His, lying 

 near the central cavity of the neural tube, 

 along the membrana limitans interna, 

 are not at all to be considered as a special 

 type of cells in contrast to the main 

 epithelial part of the medullary wall. 

 They are nothing else than epithelial cells 

 in process of continuous proliferation and 

 serve in the earliest stage of develop- 



