4OO J. SEILER. 



inferred from its relation to the slightly developed spindle-thick- 

 ening. As the daughter-chromosomes move towards the spindle- 

 poles the X-chromosome is found to lag behind, in some cases 

 towards the outer plate, in others towards the inner. In Fig. 4 

 it is seen wandering inwards, in 5 outwards, in 6 and 7 inwards, 

 in 8 outwards. During the interkinesis it is only occasionally 

 recognizable (Fig. 9). In the metaphase of the second division 

 (Fig. 10) it has without exception overtaken the autosomes and 

 thenceforwards shows precisely the behavior of an autosome. 

 Only in exceptional cases does the X-chromosome move from 

 the beginning at the same rate with the autosomes; in such cases, 

 of course, it is not distinguishable in side-views of the spindle. 



In the Psychidae, as in other cases (see Seiler, '14), chromatin 

 is in some instances eliminated in large quantities during the 

 first maturation-division, in others not at all. 



The equatorial plate of the first maturation-division in the 

 egg possesses 30 chromosomes, of which 29 are bivalent and one 

 univalent. As is to be expected, the daughter-plates have dif- 

 ferent numbers of chromosomes. If the outer plate has 30 

 chromosomes the inner has 29, and vice versa. I have tried to 

 obtain photographic proof of this, but the task is extremely 

 difficult and tedious. Each egg contains but one spindle, and 

 this must be so cut that the knife passes between the two daugh- 

 ter-plates without injuring them. Further, all the chromosomes 

 (of course in both plates) must lie exactly in one plane and at 

 right angles to the optical axis. Fig. 18 shows such an ideal 

 plate with 29 chromosomes, and this photograph alone repro- 

 duces the size-relations of the chromosomes exactly as in nature. 

 The sister-plate is not suitable for photographing. All the plates 

 photographed for this work are in themselves quite as clear and 

 demonstrative as Fig. 18. Since, however, the chromosomes did 

 not always lie in the same plane, it was necessary to turn the 

 fine adjustment somewhat during the exposure; hence the some- 

 what defective and in part ambiguous character of the figures. 

 Figs. 1 1 and 12 are two sister-plates (in each case the first number 

 designates the outer plate, the second number the inner), in 

 the anaphase of the first division. Since the chromosomes un- 

 dergo little or no change of relative position during the separation 



