4. Fortptiauzungslehre. 869 



ein zweites, untergeordnetes Zentrum (Rückenmarkszentrum) anzunehmen ist. 

 Dann treten die Fasern (bei der Ellritze [Phoxinus laevis L.] in der Region 

 dos 15. Wirbels) aus dem Rückenmark in den Sympathicus über und verlaufen 

 in diesem nach vorn und hinten, wobei sie sieb segmental (durch die Rami 

 oommunicantes) den Spinalnerven zugesellen. Die für den Kopf bestimmte 

 Partie tritt vom Sympathicus zum N. trigeminns über. (Autoreferat.) 



4, Fortpflanzungslehre, 



(Siehe auch !Nr. 1800.) 



1S84) Blacknian, M. W., Spermatogenesis of the Myriopods. VI. An 

 Analysis of the Chroraosome Group of Scolopenda heros. 

 (Biological Bulletin, 19,2. p. 13S— 100. 4 text-figs. 2 plates.) 



Authors summary: 



'The chromosome group of the primary spermatocytes of Scolopendra 

 heros is made up of sixteen bivalent chromosomes (tetrads) and one Uni- 

 valent chromosome (dyad), the accessory chromosome. 



The chromosomes show such constancy in shape in the prophase and me- 

 taphase of the primary spermatocytes, and in their relation to the mantel 

 fibers of the first maturation spindle , that they seem naturally to group 

 themselves under four distinet types. These may be designated respectively, 

 as the cross-shaped tetrads, the double V-shaped tetrads, the rod-shaped tedrads, 

 and a single-rod-shaped dyad. 



The cross shaped tetrads are six in number, and may be arranged in a 

 graded series as regards size, the difference in bulk being sufficiently great 

 to allow the individual chromosomes of this type to be distinguished. One of 

 the chromosomes of this type (the largest one) can furthermore often be 

 identified by its tendency to lag behind the others during the early meta- 

 phase. 



Five of the tetrads are of the double-V-shape. The individuals of this 

 type also may be distinguished by differences in bulk. 



The rod-shaped tetrads are present to the number of five. These show 

 constant size relations and may readily be arranged in a graded series as re- 

 gards magnitnde. One of the tetrads of this type differs from the others in 

 the form it assumes during actual division. It seems to divide transversely, 

 while the others are dividing longitudinally. 



The accessory chromosome is Univalent and passes to one of the secon- 

 dary spermatocytes without division. During the metaphase it is connected 

 by mantle fibers to only one pole of the spindle. 



As a result of the first spermatocyte mitosis fifteen of the tetrads are 

 divided longitudinally (equationally), while the one remaining tetrad divides 

 transversely (reductionally). The failure of the accessory chromosome to di- 

 vide is, also, in effect a reductional division. 



During the later stages of the first maturation division and during the 

 metaphase of the second spermatocyte, it is possible to distingnish the daugh- 

 ter chromosomes derived from the several types of tetrads. by their shape 

 and their relations to the mantle fibers. The individuals of the varions types 

 show the same size ratio as exists between the chromosomes of the firsl sper- 

 matocyte, although , of course, the actual difference in bulk is but half as 

 great. 



The above results seem to etablish as a fact , or at least as a very 

 strong probability, that the chromosomes of Scolopendra heros are distinet 



