ZOOLOGY: HEGNER AND RUSSELL 
357 
contained in the nucleus of the ultimate oogonium. He found that a 
chromatic network remains in the nucleus after the chromosomes are 
formed and that the ring results from the condensation of this network. 
Giinthert (1909) repeated Giardina's work and confirmed it in almost 
every respect. Regarding the origin of the chromatic ring, he believes 
that it may consist of chromatin that has separated from the chromo- 
somes. Debaiseaux (1909) also studied these differential mitoses in 
Dytiscus marginalis but added very little to Giardina's account. His 
most interesting conclusion is that the material of the chromatic ring 
may really be nucleolar in nature. 
Several writers had noted peculiarities in the ovarian cells of beetles 
before Giardina published the results of his investigation but did not 
work out their history. Thus Will (1886) described and figured the 
origin of the nurse cells in the beetle, Colymhetes fuscus, but his work is 
lacking in detail, and Korschelt (1886) actually observed the chromatic 
ring is Dytiscus marginalis but failed to determine its real significance. 
Since Giardina's investigations were pubHshed many attempts have 
been made to find differential mitosis of a similar sort in other insects, 
but thus far without any success. Kern (1912) found a group of gran- 
ules in the oogonia of the ground beetle, Carahus nemoralis, and a similar 
group in the oocyte of C. glabratus but none of the intervening stages 
were seen and the connection between these granules and differential 
mitoses is therefore doubtful. 
It seems particularly fortunate, considering these many failures, that 
a species belonging to another family of insects has at last been found in 
which visible substances can be observed during the differential mitoses. 
The material on which the following report is based consists of over 
thirty ovaries from the whirl-i-gig beetle, Dineutes nigrior.^ These 
were obtained by the senior author^ at Woods Hole, Massachusetts, 
on August 28, 1915. Some of them were fixed in Meves' modification of 
Fleming's solution, some in Bouin's picro-formol solution, and some in 
Carnoy's acetic-alcohol-chloroform-sublimate mixture. Longitudinal 
sections were cut 5 microns thick and stained with Heidenhain's iron- 
haemotoxylin. The general relations of the nurse cells and oocytes 
were obtained from in toto preparations. 
One of the ovarioles from an ovary of Dineutes nigrior is shown in 
longitudinal section in figure 1. It consists of three general zones, the 
terminal filament (//), the terminal chamber (tc) and the growth zone 
(gz). The anterior end of each ovariole is attached to the dorsal body 
wall by a long terminal filament made up of epitheHal cells. The 
oogonia multiply and differentiate into nurse cells and oocytes within 
