A Study of Chromosomes and Chromatin Nucleoli in Euschistus crassus. 49 
of w'hich we are at present ignorant, forces we do not expect to find in 
the cell as organs that are determining factors. 
In the present paper we shall demonstrate three structural features 
in the ceUs of Euschistus crassus which differ markedly from those hitherto 
found to be characteristic of other members of this genus. Briefly sum- 
inarized, these variations are as foUows: 
First — In the resting spermatocytes there are two chromatin 
nucleoli instead of one, and four of the chromosomes are evolved from 
these two nucleoli instead of two chromosomes developing from one 
nucleolus as is typical of other Euschistus species. 
Second — There is a large chromatic nucleolus in the germinal 
vesicle, a feature we have been unable to demonstrate by the same techni- 
que in other Euschistus species. 
Third — The number of somatic chromosomes typical of Euschistus 
crassus is twelve instead of fourteen, the number characteristic of many 
other Euschistus species. 
Material. 
The material used for our work on Euschistus crassus was collected 
in Southern Pines, North Carolina by Mr. A. H. Manee, and living spe- 
cimens were forwarded to us at intervals during the spring and summer. 
Some of the mature specimens were killed at once, while others were 
reserved for breeding in the laboratory. We succeeded in raising a 
large number of these insects, thus securing practically an unlimited 
supply of aU the stages selected for Investigation. 
The photographs we have chosen to illustrate this paper were se- 
lected from one hundred and twenty-four taken during the past few 
months as a record of our work on Euschistus crassus. In addition to 
these we have one hundred and seventeen photographs of other forms 
taken during the same period. This photographic work perhaps sug- 
gests a time consuming occupation but as a matter of fact these photo- 
graphs can be taken with very httle interference with the routine labora- 
tory work. 
We keep a simple vertical camera, with a microscope used exclusively 
for photography, set up ready for use in one of our laboratory Windows. 
At convenient moments a preparation can be transferred to this 
microscope and photographed in a very few minutes, thus half a dozen 
photographs can be taken at odd moments during the morning’s work, 
and these exposed plates can be developed at some convenient time, or 
this part of the work can be done by any experienced photographer. 
Archiv f. Zellforschnng. IX. 4 
