Recicil Traclieal Gi/ls. 217 



IV. The Rectal Tracheal Gills of Imago ready to 



emerge. ') 

 Surface Observation. 



First of all there comes to oiir iiotice a coiisiderable changc in 

 the digestive caiial. The Oesophagus is followed by a part iiistead of 

 two, vvhich is regarded either as the crop or the proventriciilus; the 

 growth of the stomach and ileum is comparatively slight, but one can not 

 overlook the great changes which take place in the rectum. In this 

 stage the rectum shows two distinct divisions: the anterior portion where 

 the gills develop is highly reduced in its lenght and size by the constriction 

 of intermediate parts of two double gill rows, which stand distinct from 

 cach other owing to the constriction (fig. 8 RQ). Followed this reduced 

 rectal portion, one finds a newly grown posterior piece of rectum, 

 which, in the preceding stage, was an inconspicuous part between the 

 rectal gills and the anus. This part will be called the postbranchial 

 rectum and it is this new formation which appeared during the mota- 

 morphosis by active multiplication of cells in this anal piece. Even in 

 such constricted rectal gills, the tracheal branches are still recognizablc, 

 so that it reminds us of the feature of the former stage. Only the dorsal 

 trunk is less modified than the visceral trunk which grows stouter. 



That the rectal tracheal gills are transferred, either modified or 

 immodified, to the imago, as Palmen says correct. The continuance 

 of that organ now is so conspicuous that the superficial Observation 

 above mentioned enables us to note. 



Exuviae of the Gills. 



At this stage, in the imago's body taken out from the nymphal skin, 

 we shall find a tranparent matter Coming off the rectum. This body is 

 the exuviated mass of rectal gills or cuticular integment once attached 

 to the surface of the gills. In the fixed material, leaving these gill 

 exuviae and the rectum are found the following facts: on the longitudinal 

 sections through the rectum are clearly recognizable the exuviated gills 

 filling up the rectum throughout its length and up to the ileum (fig. 9). 

 Among the foldings of the exuviae are found epithelial cells with large 

 nuclei (fig. 9 EC). This fact misled Hagen to take these epithelial 

 cells for the whole of hypodermal lining of the gill. In my opinion, 

 although they doubtless are those detached from the gills, but they are 

 not the whole of the gill structure; for the gills, though partly lost, 

 are so clearly to be conceivable in a surface Observation, that it needs 

 not to speak of an Observation of a series of sections. 



1) The material was fixed when the nymph made a slit on the thorax 

 from which it was to emerge, and through that slit the soft whitish body 

 of imago was slightly visible. 



