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THE AMERICAN NATURALIST ' [Vol. LI 



lations between this problem and the larger problem of 

 heredity and development are very close indeed. The 

 study of lioredity is concerned not only with the adult 

 Miiininl. I)iit ;ils() with every stage in the development of 

 llic iulult the fertilized egg, or embryo, or larva that 



ai'ix'^ iVoni il, is an individual just as is the fully devel- 

 oped .niiiiial. 'riic oi-gaiiization of the fertilized egg is 

 tlic i('>ult of the inocosses of differentiation that take 

 place at cadi stauc in the history of the egg and sperm 

 fi-oiii tlic lime tlic pi'imordial germ cells are segregated 

 until the liiiilily specialized gametes have become fully 

 rm iiuMl. The ) .cried extending from the formation of the 

 priiiiei-dial ueiit> cells to and through the growth period 

 of tlic gametes is one of the least known in the entire his- 

 tory of tlie individnal. Tt is nevertheless a most im- 

 p,()i1aiit pciiod. for dui'ino tlii> time, at least in the insect 

 eua-. tlic princii)al axes of the individual are established 

 and different kinds of cytoplasm are elaborated and lo- 

 calized tliat are predetermined to form definite parts of 

 the embryo. 



The stau-es in the genn-coll cycle in insects belonging to 

 different orders, families, uoiiera or species are often 

 (piile different, as is to he expected, hence the data on 

 ^\hicli ihi^ papei- i^ ])aM"<l wci-e derived from the study of 

 a f imihcr of .p,..-i..^. On tlii^ a<-cn,n,t it ^eem^ best to 

 -i\-e ail ;dM'i(hcd dc^oapt ion of tlic o-ei-m-c<']l cNcle in one 

 uroup and ihclndc. wliei-ever nece-vary. data deiaved from 

 the stnd>- of other groups. The pi'incipal work has been 

 carried on with representatives of the orders Diptera, 

 II\ Micnoi»tcra and Coleoptera, and of these, the order 

 Coleoptera ha> furnished the best material for experi- 

 mental i.nrpose>. ^ AVe will select, thei-efore, the eggs of 



2. 77/r Shu,hn, fin I>,^<<t nl tJte Timc of Dcpo- 



At th(^ time of dctM.dti-ii ( KIu. 1 ) tlic beetle's egg con- 

 si>t- ' ■ ■ c.;i.i,| ;i -,di-tance which is used 



