464 N. M. Stevens 



In the Diabroticas they are present with a larger unpaired hetero- 

 chromosome, and there is no evidence that they are ever united 

 w^ith it. The most puzzHng characteristic of the supernumeraries 

 in the Diabroticas is the fact that they may in the same individual 

 divide in either maturation division, and v^hen two, three or four 

 are present, each one may divide in either spermatocyte division, 

 thus giving great diversity in the chromatin content of the sper- 

 matozoa. In Metapodius the supernumeraries are described as 

 dividing in the first division. 



Occasionally, as in Figs. 64 and 73 two of the supernumeraries 

 seem to be paired in the metaphase of the first division, but this is 

 probably accidental, as it is not constant in any individual. 



The only other known case among the Coleoptera at all resem- 

 bling this is that of the steel-blue flea-beetle, Haltica chalybea, 

 which has a large and a small heterochromosome which are often 

 widely separated in the metaphase of the first spermatocyte (fig- 

 ures not yet published). In the anaphase, however, • the two 

 heterochromosomes are found between the two daughter plates, 

 and one goes to each second spermatocyte. This is merely a 

 case of late pairing and the distribution of the division products 

 of the two heterochromosomes to the spermatozoa is the same as 

 in other cases of an unequal pair of heterochromosomes. 



The first lot of Diabrotica 12-punctata were dissected out and 

 all fixed together, so there was no opportunity to connect differ- 

 ences in the germ cells with diff'erences in external characters of 

 the insects, if such existed. In the Cahfornia material obtained 

 in December, 1906, and March, 1907, from Miss McCracken, 

 each beetle, after dissecting out the testis or ovary, was preserved 

 in alcohol, and later placed in the vial with its germ gland. In 

 the December lot there was a difference of i mm. in the length of 

 the Elytra, some measuring 4.5 mm., others 5.5 mm. All of the 

 smaller beetles had the odd heterochromosome only, the others 

 one supernumerary additional; and it was quite naturally sup- 

 posed that there might be two distinct species or varieties, one of 

 which had only the large unpaired heterochromosome, the other 

 an unequal pair of heterochromosomes. In the March lot, one 

 exception occurred — a small beetle had the additional small chro- 



