THE ALIMENTARY CANAL 89 



ectoderm. Richards' study of five species of Arctiidae belonging to 

 three genera conchides that 



either the mid-gut, despite its final similarity within individual orders of 

 insects, may arise in some cases as an entodermal derivative and in other cases 

 as an ectodermal derivative ; or else we must look upon the determination of the 

 mid-gut as a purely physiological process; to borrow Driesch's terminology, 

 "as a function of the position within the whole." ... the latter interpretation 

 seems much superior to the former in the light of the great diversity shown by 

 closely related insects, and from the standpoint of modern views of develop- 

 mental processes in general. 



COLEOPTERA 



In the Coleoptera, development of the mid-gut epithelium from the 

 entoderm as well as from the ectoderm has been described. The follow- 

 ing table separates the members of the order according to the supposed 

 origin of the epithelium : 



1. Mid-gut epithelium an entoderm derivative: Doryphora {Leptinotarsa) decemlineata 



(Wheeler, 1889), Donacia crassipes (Hirschler, 1909), Euryope terminalis and 

 Corynodes pusis (Paterson, 1932, 1936), Tribolium conjusum (Hodson, 1934), 

 Meloe proscarabaeus (Xusbaum, 1888), and Calandra callosa (WraA% 1937). 



2. Mid-gut epithelium an ectoderm derivative: Chrysomela hyperici (Strindberg, 



1913); Chrysomela menthastri, Clystra laeviuscida, Gastrophysa raphani, Lina 

 populi and L. tremulae, Agelastica alni (Lecaillon, 18986); Tenebrio molitor 

 (Saling, 1907); Meloe violaceus (Czerski, 1904); Hydrophilus sp. (Deegener, 1900); 

 Calandra oryzae (Mansour, 1927). 



In Donacia crassipes and Meloe proscarabaeus, listed in the first group, 

 the mid-gut epithelium is said to arise from a middle entodermal strand 

 as well as from the paired ribbons of the bipolar rudiments. In Euryope 

 and Corynodes, the species studied by Paterson, also in the first group, 

 the epithelium is built up solely from a middle entoderm strand. Bruchus 

 quadrimaculatus (Brauer, 1925) might be placed in either division. 



Calandra oryzae, a species in the second group, has been studied by 

 Mansour (1927) and by Tiegs and Murray (1938). The latter do not 

 commit themselves as to which germ layer gives rise to the mid-gut 

 epithelium except to say that it is not entodermal. Mansour (1927) 

 from his study of this species concludes that the entodermal cells of 

 insects are budded off into the yolk from the walls of the ventral groove 

 or from thickenings in the blastodermal wall; further, that in Calandra 

 oryzae and most Pterygota the entodermal cells do not give rise to any 

 larval or invaginal structures but that the mid-gut epithelium is derived 

 from the inner ends of the stomodaeum and proctodaeum and is therefore 

 of ectodermal origin. 



An examination of the foregoing tabulation reveals that the families 

 Chrysomelidae, Tenebrionidae, Meloidae, and Curculionidae, as well as 



