GASTRIC CyECA OF THE HETEROPTERA. 137 



is not clear, unless this is due to a specialization of the alimentary 

 canal correlated with the strictly predaceous habits of these 

 insects. In this connection, it is of interest to note that the caeca 

 are invariably absent in all the strictly predaceous Heteroptera. 



The Scutellerinae, judging from their caecal equipment, are 

 evidently close to the primitive Pentatominas. Of the Cydninae 

 but a single male of Amnestes pusillus has been examined; and 

 as the caeca were apparently absent in this specimen, this sub- 

 family may be further removed than even the Thyrecoridse, 

 although no generalization can be made from this one dissection. 



In regard to the function of the caeca of these insects, it can 

 only be said that no digestive function has been discovered, and 

 that the food mass in process of digestion apparently never gets 

 beyond the third stomach. 



This, together with the fact that these organs are located at 

 the extreme lower limit of the digestive portion of the gut and 

 are apparently in process of elimination, would seem to show that 

 they possess no important digestive function, although the great 

 development of these structures in forms like Brochymena would 

 certainly suggest this. 



It seems not improbable that the present function of the 

 caeca of the Heteroptera is merely to provide a safe place for the 

 multiplication of the normal bacteria of these insects. 



It was originally planned to include in the present paper a 

 discussion of the histology of the different divisions of the ali- 

 mentary canal, as well as a comparative treatment of the caeca 

 from the different insects studied, having in mind particularly 

 the bearing of these structures on the iclationships and classifica- 

 tion of the different groups of Heteroptera; but owing to lack of 

 available space this aspect of the work will have to be omitted 

 for the present and reserved for publication at another time. A 

 glance, however, at the accompanying illustrations of typical 

 caeca selected from a few of the Heteroptera dissected, will show 

 very well the range of development of these organs in this group, 

 and also the possibilities that open up for a very thorough and 

 complete survey of the caeca in these insects. 



Some idea of the ground already covered in this phase of 

 the work can be had from the following list of species, representa- 



