NEW TYPES OF CHROMOSOME DISTRIBUTION. 129 



Conorhinus sangiiisiigns Lee. 1 



Couorhinits gives an additional verification of the type de- 

 scribed in Fitchia. The number and size relations of the chromo- 

 somes are somewhat different. The spermatogonial divisions 

 (Fig. 4, A and B} show 23 chromosomes, two of which are dis- 

 tinctly smaller than the others. In the metaphase plate of the 

 first division (Fig. 4, C and D) there are 13 chromosomes, ten 

 of which must be bivalent and three univalent as there are 23 

 in the spermotogonia. In this division, contrary to what is 

 found in all other cases, the bivalent chromosomes form an irreg- 

 ular ring and the differential chromosomes, which are easily 

 recognized by their size relations, take up a central position, but 

 all lie in one plane. All the chromosomes divide equally in this 

 division, so that each secondary spermatocyte receives 13 chromo- 

 somes, the arrangement of which is somewhat different from that 

 in the first division. There are ten in the ring, but the differ- 

 ential chromosomes which occupy a central position, show a re- 

 grouping as in Fitchia. The large and one small one lie in the 

 same plane, but the second small one is either above or below 

 the other two, forming the characteristic triad group (Fig. 4, 

 G and H, side views of the second division, metaphase). The 

 ten chromosomes in the ring divide equally, while the chromo- 

 somes of the triad group separate, two going to one pole and the 

 other to the opposite pole. Fig. 4, / and /, representing two 

 anaphases from the same spindle, show the chromatin content of 

 the two class of spermatozoa, which contain respectively 13 and 

 14 chromosomes. 



The size relations of the differential chromosomes in the three 

 forms illustrating this type of distribution are different in each 

 case. In Fitchia the one which goes to the male-producing pole 

 is slightly larger than the other two. In Rocconota all three are 

 practically of the same size and in Conorhinus, one of the two 

 which goes to the female-producing pole is larger than the other 

 two. 



The history of the differential chromosomes in the growth 

 period has been followed as far as material permits. Sometimes 



1 This identification is somewhat doubtful as all my specimens are immature. 



