136 HUGH GLASGOW. 



be regarded as more highly specialized forms in which the caeca 

 have entirely disappeared. This view seems to agree in essentials 

 with the best grouping of the Heteroptera, and Mr. Hart, who has 

 kindly compared the evidence presented by the structures with 

 the principal systems of classifications that have been proposed 

 for these insects, finds that the relationships indicated by these 

 structures agree remarkably well with the grouping of the 

 Heteroptera as proposed by the great European hemipterist, 

 Stal, although suggesting relationships decidedly at variance 

 with those that have been assumed by certain American workers. 



The view that the complex types of caeca should be considered 

 the more primitive is also strongly supported by embryological 

 evidence. 



Upon dissecting the embryo of the pentatomid, Murgantia 

 histrionica, a day or more before time for hatching and shortly 

 after the midgut had formed, the caecal region was found to be 

 represented by a comparatively long, pink section of the intestine, 

 upon which the four rows of minute caeca were appearing, each 

 caecum originating as an independent evagination of the wall of 

 the embryonic intestine. 



A similar study of the embryonic gut of such Lygaeidae as 

 Blissus leucopterus would be very desirable, in order to see if 

 the typical grouping of the caeca of the Blissinae is not merely a 

 specialization from forms such as those in the Pachygronthinae. 

 An examination of the embryonic caeca of the Thyrecoridae as 

 well as of the Cidnidae, would also be worth while, as it is here 

 that we should expect the actual transition to take place from 

 the four-rowed form of the typical Pentatomidae to the forms 

 with but two rows, if the caeca in the Heteroptera are really 

 being reduced in complexity. 



If this view is correct, and it can hardly be questioned, then 

 the Asopinae could not be considered the more primitive type 

 of the Heteroptera, as has been suggested by Kirkaldy, but would 

 have to be considered a much more specialized group than the 

 Pentatominae, in which the caeca reach their greatest develop- 

 ment in such forms as Brochymena quadripustula, where there 

 may be as many as 1,400 caeca in the entire system. 



Just why the caeca should drop out so suddenly in the Asopinae 



