J. W. H. Harrison and L. Doncaster 235 



Further, in the maturation divisions, as was found by Federley in 

 hybrids of species of Pt/(/aera\ most of the chromosomes are unpaired 

 and divided singly, so that the spermatocyte divisions have nearly as 

 many as the spermatogonia and oogonia, but my results differ from 

 those of Federley in the fact that a few of the hirtaria chromosomes 

 pair with some derived from the zonaria parent, and that there is a 

 distinct synapsis stage in the prophases of the maturation divisions. 

 The methods of preservation, etc., employed were the same as those 

 described in my papers on gametogenesis of Abraxas, with the exception 

 that the gonads were dissected out in water, which I have found, since 

 those papers were written, to give better results than Ringer's fluid. 

 The material of the pure species was obtained from quite young pupae 

 purchased from Mr L. W. Newman ; that of the hybrids, from larvae 

 and pupae given me by Mr Harrison. 



1. The chromosomes of Z. {B.) hh'taria. 



{a) Oogenesis. I have very few satisfactory figures of the oogonial 

 divisions, but there seems to be little doubt that the chromosome number 

 is 28. Plate XVIII, fig. 2 shows an oogonial equatorial plate, with 28 

 chromosomes varying considembly in size, and including six which are 

 noticeably smaller than the remainder. I have one figure in which in 

 addition to a similar group of 28, there is a body just outside the circle 

 which might be a chromosome. I am inclined to believe that it is not 

 a chromosome, but an extra-nuclear body (fig. 1). 



A typical synapsis stage succeeds the last oogonial divisions, followed 

 by a growth phase of the oocytes in which a relatively small number of 

 fairly thick threads form a spireme. As the oocytes enlarge, these 

 threads shorten in the usual way, and become faintly double, and by 

 the time they have become elongated rods about thirteen can be counted 

 (fig. 3). They then contract still further to double, or often faintly 

 quadruple, bodies, of which again about thirteen may be counted. 

 Meanwhile a chromatin-nucleolus has been conspicuous, and still remains 

 much more sharply defined than the other chromosomes. It is com- 

 pound, and in the many figures is seen to be composed of four parts, two 

 small and two larger. The latter are frequently seen to be unequal in 

 size. If the chromatin-nucleolus may be regarded, as in other forms, as 

 a " sex-chromosome " there is thus perhaps an indication of its being 

 unequally paired. There is no regularity, however, in its appearance ; 

 the parts may be together or widely separated, and are sometimes seen 



1 H. Federley, Zeitachr. f. indukt. Abstamin. unci Vererhungslehre, ix. 1913, p. 1. 



