I 



NO. 10 MORPHOLOGY OF GN ATHOTRICIIUS SCHEDL 8l 



The oesophagus is a short tube of about equal diameter through- 

 out. The caudad widened part, which is also encircled by strong- 

 muscles, may correspond to the united crop and proventriculus. 



Mid-intestine. — The mid-intestine occupies the greatest area of the 

 whole digestive system of the larva. The ventriculus is pearlike in 

 shape, having the blunt end anteriorly. The gastric coeca are not so 

 densely placed and are smaller than in the adult. The posterior tube is 

 distinctly separated from the ventriculus. It gradually decreases in 

 diameter towards the apex and bears on its caudad end the Mal- 

 pighian vessels. These originate as a single tube and become divided 

 shortly after their origin. Three pairs of vessels are present. 



Hind-intestine. — As in the adults the hind-intestine forms a loop. 

 The hind-intestine is encircled by ring muscles. The small and large 

 intestines are not very distinctly separated from each other. More 

 clearly defined is the rectum. The latter is distinctly wider than the 

 rest of the hind-intestine, and the muscles encircling it are much 

 more strongly developed. 



From the anus originates a glandlike structure which is strongly 

 widened distally. This evidently represents the ectodermal part of the 

 reproductive organs of the adult. See also the discussion of the 

 reproductive organs of the adult. 



THE PUPAE 



In the study of the pupa of Gnathotrichus, special attention was 

 given to the changes of the setal arrangement from larva to pupa. 

 The only illustration of a pupa of the Scolytidae showing the setal 

 arrangement was found in the monograph of the genus Dendroc- 

 toniis by Hopkins (38). It seems that Hopkins, who has usually 

 overlooked the setae of the larva, did not realize the origin of the 

 setae of the pupa, which he called spines. Russo, on the other hand, 

 shows plainly the setae of the larva but has ignored those of the 

 pupa. In fact, it is a difficult undertaking to study the setae of such 

 small larvae or pupae. In Gnathotrichus, it is not possible to find the 

 setae by working with a binocular but slides had to be made and those 

 carefully examined under the microscope. The following discus- 

 sion is illustrated by figure 40. The setae are only barely visible 

 soon after the last molting of the larva. In the young pupa they are 

 most distinct before the pupa starts to become the mature color, and 

 they disappear gradually with the ripening of the adult. 



