134 HUGH GLASGOW. 



extending along opposite sides of the tubular fourth stomach, in 

 varying degrees of complexity, from an extremely simple type 

 found in the Pyrrhocorinae (Plate IV., Fig. 10) (in which the 

 caecal equipment consists merely of a double row of a half dozen 

 or more comparatively minute outpocketings at the extreme 

 posterior end of the tube, and this only in the female), to the 

 highly complex arrangement met with in the Largiinae (Plate 

 VI., Fig. 1 6) and in many of the Coreidae and Lygaeidae (Plate I., 

 Fig. i) (where the caeca may take the form of two rows of short 

 closely packed units often numbering into the hundreds), or 

 they may be arranged in definite groups of extremely long 

 finger-like tubes, on opposite sides of the intestine, much fewer 

 in number than in the forms just mentioned, but compensating 

 largely for the loss in numbers by a very marked gain in the 

 diameter and length of the individual caeca. In all of these 

 highly modified forms the typical arrangement is maintained. 

 In the other group, including the Pentatomidae, with the excep- 

 tion of the Asopinae in which the caeca are absent, there are four 

 rows of short, uniform, closely set, sac-like structures ranged 

 along the tubular portion of the fourth stomach; and this ar- 

 rangement is adhered to with remarkable uniformity in all the 

 typical Pentatomidae so far examined. 



Before discussing the various forms of caeca in detail, it might 

 be well to consider the probable origin and course of develop- 

 ment of these complex organs in the different divisions of the 

 Cimicoidea. 



Recognizing the Pentatomidae as the more primitive Heteroptera 

 then, according to the view expressed by some authorities, the 

 Asopinae might be taken as representing the stock from which all 

 the other Heteroptera developed. We find in examples of this 

 subfamily, such as Podisus maculiventris (Plate II., Fig. 5), 

 that the caeca are wholly absent, and that the fourth stomach 

 consists merely of a short neck connecting the third stomach with 

 the ileum. If we consider the Asopinae as representing a type 

 which existed previous to the first appearance of caeca in the 

 Heteroptera, then the Thyrecoridae should logically come next in 

 the series, as they form a perfect connecting link, so far as the 

 caecal structures are concerned, between the typical Pentatomidae 



