GASTRIC OECA OF THE HETEROPTERA. 



tests, if it were not that there is a more or less complete transition 

 from it to the typical bacterial forms' of such insects as Anasa 

 tristis and Euschistus servus. The transition forms are found in 

 such pentatomids as Brochymena quadripnstnlata, Proxys punctu- 

 latus and Peribalus limbolarius. 



There is little to characterize the csecal organism of Murgantia 

 except its irregularly twisted and remarkably contorted form, 

 which is retained not only in the caeca, but also in the embryo 

 during its passage through the egg. The irregular form of this 

 organism as it occurs in the caeca, which is much more suggestive 

 of spirochaetes than of bacteria, does not lend itself well to 

 description and the reader will perhaps get a better idea of this 

 by glancing at the figure referred to above. 



These organisms vary from small, contorted individuals, 2 or 

 3 microns long to huge, irregularly bent bodies, not infrequently 

 measuring 100 microns or even more in length by 1.5 to 3 microns 

 in diameter. The most common form is 10 to 15 microns long 

 although examples 25 to 30 microns long are common. The 

 diameter of a single individual may vary considerably at different 

 points and frequently such elements with a very decided bulb- 

 like enlargement at one end, or even in the middle, occur. Others 

 which are decidedly swollen throughout and which stain with 

 great difficulty are fairly common, while often an end of one of 

 the long individuals will take the stain readily, the remainder 

 staining weakly or not at all. On the whole these organisms 

 from Murgantia strongly suggest degenerating, involution forms, 

 and this is probably their true nature. 



FUNCTION AND PHYLOGENETIC SIGNIFICANCE OF THE CECA OF 



THE HETEROPTERA. 



The midintestine of the Heteroptera is typically divided into 

 four rather clearly defined regions which, for convenience, may 

 be termed the first, second, third and fourth stomachs. All 

 four can usually be made out, although in some of the more 

 highly specialized groups certain of these divisions, especially 

 the two posterior ones, may be very greatly reduced. 



At its anterior end the midgut is uniformly dilated, forming a 

 capacious, thin-walled, bag-like structure, capable of consider- 



