(,\STRIC CECA OF THE HETEROPTERA. 135 



with their four rows of caeca and the Lygaeidae, Coreidae and Pyr- 

 rhocoridae with their two rows. In this family, as represented by 

 TJiyrecoris unicolor (Plate I., Fig. 3), the caeca might well be 

 regarded as showing a very primitive condition, since they appear 

 in a double row of very blunt evaginations from the wall of the 

 gut which shows no indication of the distinct, narrow ducts so 

 common in most of these insects, and which might readily be 

 imagined as in process of formation directly from folds or wrinkles 

 in the intestinal wall. No direct transition has as yet been seen 

 between the double row of caeca of TJiyrecoris and the quadruple 

 arrangement in the typical Pentatomidae; but it can hardly be 

 doubted that in some of the Thyrecoridae, or perhaps in the 

 Cydninae, forms will be discovered in which the doubling of the 

 rows of caeca is actually taking place. The specimens of Thyre- 

 coris examined, and from which the drawing was made, were 

 males; and as the caeca uniformly show a more complete develop- 

 ment in the female than in the male, I should not be surprised to 

 find at least indications of a third and fourth row when this sex 

 is examined, although in the male the intestine does not show 

 the slightest indication of this, even in sections. 



This arrangement apparently does very well in the Penta- 

 tomidae; but when the other families in which caeca occur are 

 considered, a number of almost insurmountable difficulties are 

 encountered. 



It is easy to imagine how the complex types of caeca in the 

 Coreidae, Lygseidae, and Pyrrhocoridae could have originated from 

 a common form like that of Thyrecoris, but the fact that in each 

 of these families a number of species occur which are obviously 

 not primitive, but in which the caeca are wholly wanting, is 

 decidedly confusing when a progressive development of the caeca 

 is considered. 



It is probable that these organs, instead of representing a con- 

 tinuous line of development in the existing Heteroptera from 

 simple to complex types, are really primitive, ancestral organs, 

 as has been suggested by Mr. C. A. Hart, of the State Laboratory 

 of Natural History, which are actually in process of elimination 

 as the group advances in specialization; and that the confusing 

 cases met with in the three families just mentioned should really 



