GASTRIC C/ECA OF THE HETEROPTERA. 133 



Thyrccoridae, Pyrrhocoridae, Lygaeidae, and the Coreidse. In 

 these families, whenever the cseca are present, the fourth stomach 

 occupies a prominent place in the midgut in the form of a long, 

 slender tube, and it is on the posterior end of this tube that the 

 pouch-like caeca are borne. In these forms the tubular part of the 

 fourth stomach is regularly somewhat dilated immediately below 

 the third stomach, and this tendency is occasionally exaggerated 

 to such an extent that in certain species, as in Blissus leucopterus, 

 a bulb-like structure may be formed at the anterior end of the 

 tube nearly as large as the third stomach itself, but this dilation 

 is not constant in size and does not represent one of the typical 

 divisions of the midintestine. 



The ileum in the Cimicoideae presents a characteristic modifica- 

 tion which may well be mentioned here, for instead of continuing 

 as a simple tube from the point of insertion of the Malpighian 

 vessels to the rectum, it forms a thin-walled, bladder-like reser- 

 voir, of various shapes, into which the four Malpighian tubes 

 empty, each tube usually being inserted singly, about half way 

 down on the side of this bladder-like ileum. The ileum opens 

 by way of a narrow, valve-like constriction into the capacious, 

 thin-walled, muscular rectum, which may or may not be pro- 

 vided with a large anteriorly, projecting cul-de-sac, depending 

 on whether the ileum opens directly into its anterior end or 

 further down on its side as it does in some of the Coreidce. The 

 walls of the rectum are very elastic and its size varies greatly. 

 When not gorged it may be no larger than the third stomach 

 and still be smoothly rounded, while in the same species it is 

 occasionally found so greatly distended that it occupies most of 

 the abdominal cavity, although this condition is decidedly 

 exceptional. 



As has already been stated, the caecal appendages of the 

 Heteroptera are apparently confined strictly to certain families of 

 the Cimicoideae; and while these organs at first appear to form 

 a number of widely different types, they are found upon closer 

 examination to fall regularly into two clearly defined groups 

 ranging from very simple to highly complex forms. In one of 

 these groups in which the Pyrrhocoridae, Thyrecoridae, Lygaeidae, 

 and Coreidae may be included, the caeca are arranged in two rows 



