342 



INSECT A. 



Many authors, however, differ greatly as to the origin of the fat-body. 

 Doiirn, Tichomiroff (No. 79), and, recently, Will have derived it from 

 the yolk-cells, while other authors have claimed an ectodermal origin for it. 

 Among these latter are Korotxeff (No. 47) and Schaffer (No. 124a), who, 



in confirming former statements made by 

 Weismann, trace back the fat-body of Musca 

 to growths from the tracheal matrix and 

 partly from the hypodermis. Graber also 

 (No. 31) has recently maintained the ecto- 

 dermal origin of the fat-body in Hydrophilm 

 and Stenobothrus. As regards Hydrophilus, 

 we are unable to agree in this view. 



I. Genital Organs. 



The published accounts of the develop- 

 ment of the genital organs are, with the 

 exception of those relating to the pecu- 

 liar and specialised conditions in the 

 Aphidde and Diptera, much scattered 

 and for the most part fragmentary and 

 unsatisfactory. We must refer the 

 student to the works of Balbiani (No. 

 3), and Witlaczil 

 —om, (No. 98), and especi- 

 ally to those of Hey- 

 mons (No. 43). We 

 are able, however, to 

 gather (chiefly from 

 the writings of Grassi, 

 No. 32, Heider, No. 

 38, and Wheeler, No. 

 95) that the genital 

 glands are mesodermal 

 in origin, and develop 

 from the wall of the 

 coelomic sac. The 

 development of the 

 efferent ducts has been 

 best described by 

 Nusbaum (No. 61) and 

 Palmen (No. 162). 

 Heymons (No. 43) has 

 recently published accounts of the rise of the genital organs in 



Pie. 10S. — Lateral sagittal section through the abdom- 

 inal part of a germ-band of Phgllodromia gerw.av.icd after 

 the primitive segments have completely formed (after 

 Heymons). 1-7, tirst seven abdominal segments, from 

 the eighth (8) to the terminal segment (es) the abdominal 

 germ-band is flexed ventrally ; am, amnion; c, coelomic 

 sac ; d, food-yolk ; es, terminal segment ; gz, genital 

 cells, lying partly in the dissepiments and partly in the 

 wall or the cavities of the primitive segments. 



