572 A. C. WALTON 



The ootids and the spermatids thus possess the haploid num- 

 ber of dj-ad chromosomes (fig. A, 9 a). After the formation of 

 the first segmentation spindle, there is once more the diploid 

 number of chromosomes, last seen in the oogonia and sperma- 

 togonia. The two first cleavage cells thus have either thirty or 

 thirty-six dyad chromosomes — depending on the type of the 

 fertilizing sperm, that is whether it had twelve or eighteen 

 (twelve plus the 'X' group of six) chromosomes — each of which 

 has the characteristic transverse constriction or Querkerbe (fig. 

 A, 9 a). In the cleavage cell which is the forerunner of the 

 propagation cells, the chromosomes do not change, but retain 

 their dyad form during subsequent divisions. During the first 

 division of each of the soma cells of the first five generations 

 after being separated from the 'stem' cell, a very different 

 phenomenon appears. Each of these soma cells, in their first 

 (or second) division after separation from the ' stem' cell, under- 

 goes 'diminution' of chromatic material. From one-third to 

 one-half of the chromatin material is cast out into the cytoplasm 

 and disintegrates. The remaining chromatin, however, does not 

 resume its original state in thirt}^ or thirty-six smaller dyad 

 chromosomes, but appears in the form of sixty or seventy-two 

 monad chromosomes, practically spheroidal in shape (fig. A, 10 a; 

 10 h). It seems most probable that these small spheroidal chro- 

 mosomes have arisen by a process of division, or fragmentation, of 

 the original chromosomes along the plane of the Querkerbe. Thus 

 it may be that the Querkerbe, since it does not represent a 

 former plane of telosyndesis, or parasyndesis, nor yet the plane 

 of a future maturation division, — Agar ('12) and Kornhauser ('15) 

 having shown that Haecker ('95, '11) and his students were 

 wrong in supporting such views, — is an indication of the plane 

 along which the final division of the chromosomes into their 

 simplest components will take place. The presence of the 

 Querkerbe may, then, perhaps, be taken as an indication of the 

 presence of plurivalent chromosomes in the sex cells of animals, 

 perhaps also in plants. As yet, however, the actual presence of 

 plurivalent chromosomes has not been demonstrated in all 

 forms which show the Querkerbe. Another fact, which may or 



