SYNAPSIS AND CHROMOSOME ORGANIZATION 485 



The differentiation on the basis of size is not always easy to 

 make. This difficulty is made more apparent by the differences 

 between the order used on this plate, where the accessory is 

 made number 3, and the order used by Carothers, who made 

 the accessory number 4. Such differences, however, are without 

 significance so long as other means of identification are avail- 

 able to obviate confusion. The supernumerary is placed at the 

 top of the plate to avoid any possibility of its becoming con- 

 fused with the smaller tetrads. From left to right are shown 

 successive stages in the transformation of the spireme segments 

 to tetrads, and their condensation, final orientation, and partial 

 division in the spindle of the first maturation mitosis. 



A glance at the metaphase figures shows that the complex of 

 this individual consists of four pairs of atelomitic chromosomes 

 (nos. 7, 10, 11, 12), five pairs of telomitic ones (nos. 2, 4, 5, 6, 

 9), two heteromorphic pairs (nos. 1 and 8), the atelomitic acces- 

 sory (no. 3), and the supernumerary. In other individuals of 

 the species the relative numbers of pairs of atelomitic, telomitic, 

 and heteromorphic pairs may be different, as found by Carothers 

 and described by her. 



It is not possible in every case always to identify each chromo- 

 some in a cell. This is due to similarities of size and organiza- 

 tion. Chromosomes 11 and 12, for example, appear very similar 

 in size and organization in the earlier stages, so that it is not 

 always possible to tell which is which. In the metaphase and 

 anaphase, however, these two are distinguishable by the dif- 

 ferent proportions between arm-lengths of the Vs. Number 

 12 has the greatest disproportion between arm lengths; in num- 

 ber 11 the disproportion is less, and in number 10 still less. 

 The proportions between arm-lengths for these atelomitic 

 chromosomes can the more readily be determined by reason 

 of the occurrence in many of the metaphase examples of con- 

 strictions or transverse clefts at the points of spindle-fiber at- 

 tachment. Such clefts are to be seen, for example, in cells E, 

 F, and G for chromosomes number 11 and 12, and cells E and 

 F for number 10. Such clefts or constrictions (marked b in 

 the figures) can sometimes be distinguished in the earher stages 



