Rectal Tracheol Oills. 223 



grobule. Biit it is evident that they are quite homologous with other 

 coiinective tissue (and triie fat cells) both in being fornied froin mesodermal 

 cells in early stagcs of development, so that they niay be called nierely 

 connective tissue cells, as Faussek i) describes as follows. 



„Was das Bindegewebe, das den inneren Raum der Darmkieinen 

 füllt, anbelangt, so besteht es aus mit Kernen und Hüllen versehenen 

 Zellen, welche aber nicht regelmäßig im Gebiet der Darmkiemen verteilt, 

 sondern in einzelne Komplexe von runder oder länglicher Form zu- 

 sammengefaßt und von einer dünnen, deutlich sichtbaren 

 Hülle (Membrana propria?) umgrenzt sind". He observed, 

 therefore, with certainty the membranous covering in the periphery of the 

 cell-complex and supposed them to be the Tunica propria. I have, 

 however, not detected such a membrane except the basement membrane 

 underneath the epithelium. to which 1 have repeatedly referred. Though 

 the functions of these peculiar cells are still obscure, it seems very probable 

 that they serve in means similar to other connective tissues and that they 

 have other functions, which are noy yet explained. 



VIII. Summary. 



1. The rectal tracheal gills undergo striking changes during a 

 remarkable short time, and these changes are necessary to the Supplement 

 of the wounded portion of the rectal wall by ecdysis for the insect maintain- 

 ing the same condition of life without pupal resting stage. 



2. At the last ecysis, the epithelial cushion is detached from the 

 basement membrane and subsequently is cast out of, the adult body, 

 together with the cuticular coating of the gills, but they never include 

 the whole of the branchial epithelium. The view of Hagen who denied 

 Palmen's opinion is, therefore partly correct. 



3. The falling off of the epithelial cushion is a destruction of epi- 

 thelial wall of the rectum; this destruction gives rise to the new for- 

 mation of epithelium and opens the path for the germinal connective 

 tissue cells wandering out, and from these cells is formed finally a new 

 supporting element under the newly formed epithelium. 



4. The gill lamellae are transferred, with little modification, 

 to the adult body. So the view of Palmen is proved partly to be the fact, 

 as a part of the epithelial cushion is certainly thrown off at the last ecdysis. 



5. The gills are eliminated from the inner surface of the rectum 

 in consequence of Prolongation of the postbranchial rectum ; at the same 

 time, the longitudinal muscles of intermediate portions of every double gill 

 row develop enormously, and at last, six double rows are converted 

 into six pockets which open by a small path to the interior of the alimentary 

 canal. 



1) Faussek: Zeitschr. f. Wiss. Zool. XLV. 1887. p. 710. 



