160 



The Nucleus and Cytoplasm in Development 



tively, which are elaborated by such organs 

 as the Malpighian tubes and the fat bodies 

 (Beadle, '37; Beadle, Tatum, and Clancy, 

 '39). In another Drosophila case a combina- 

 tion of autonomous and dependent processes 

 has been shown to exist. The difference be- 



Fig. 4L Mosaic eye of Habrobracon juglandis. 

 Ifpper left: ivory {o*C); lower right: cantaloupe 

 {Oc). Note the wild type coloration at the junc- 

 tion of the two tissues and the decreasing wild type 

 coloration within the cantaloupe region. (After A. 

 R. Whiting, '34.) 



tween the narrow bar eye of Drosophila and 

 the normal round eye is caused in a twofold 

 way: (1) an embryonic or very early larval 

 reduction in the size of the eye disc which 

 may be an autonomous result of the geno- 

 type, and (2) a later larval interference with 

 the formation of a specific diffiisible sub- 

 stance which is instrumental in transform- 

 ing cells of the eye disc into ommatidia 

 (Chevais, '43). 



Genie action at a distance may be brought 

 about by substances whose transfer from one 

 part of the body to another is mediated by a 

 circulatory system. In some instances action 

 at a distance results from short range diffu- 

 sion of gene-dependent substances rather than 

 from equal distribution of such substances 

 throughout the body. A striking example has 

 been described in the parasitic wasp Habro- 

 bracon juglandis (A. Whiting, '34). (See 

 Fig. 41.) The normal stock possesses a black 

 eye pigment while the coloration in two non- 

 allelic mutant stocks is ivory and cantalovipe, 

 respectively. We may signify the phenotype 

 black as the genotype "not-ivory, not-canta- 

 loupe," the phenotype ivory as genotype 

 "ivory, not-cantaloupe," and the phenotype 



cantaloupe as genotype "not-ivory, canta- 

 loupe." From double nucleus eggs individ- 

 uals have been raised which carry in one 

 part of an eye the genetic constitution 

 "ivory, not-cantaloupe" and in the other part 

 "not-ivory, cantaloupe." On the whole there 

 is autonomy of phenotypic expression as wit- 

 nessed by a large ivory and a large canta- 

 loupe area. However, at the border zone 

 between the two a strip of cells is neither 

 ivory nor cantaloupe but black. This finding 

 can readily be explained if one assumes that 

 a substance produced in only one of the 

 two genetically different tissues diffuses into 

 the other and thus reconstitvites the fvill effect 

 of a "not-ivory, not-cantaloupe" genotype. 

 The black zone shows a sharp border with 

 the cantaloupe region but gradually grades 

 over an orange coloration into the ivory 

 part. The orange is known as an intermediate 

 step between fvill black and ivory pigmenta- 

 tion. From these facts and others it has been 

 inferred that the diffusible substance is pro- 

 duced in the "not-ivory, cantaloupe" region 

 by the dominant not-ivory gene. 



An unusually interesting nonautonomous 

 differentiation, also in mosaics of Habro- 

 bracon, concerns the external genitalia 

 (P. W. Whiting, Greb, and Speicher, '34; 

 Whiting, '40). Here, eggs develop occa- 

 sionally in which the mature egg nucleus as 

 well as a polar nucleus take part in parthen- 

 ogenetic cleavage. Since the diploid females 



Fig. 42. Ventral view of genitalia of a male com- 

 posed of tissues of two different sex genotypes. The 

 right outer clasper is feminized, resembling a mi- 

 nute sensory female gonapophysis. (From P. W. 

 Whiting, '40.) 



are heterozygous for a pair of genetic sex 

 "factors," and their sons are usually hemi- 

 zygous for either one or the other of the 

 sex factors, the offspring developing from 

 the binucleate eggs may be genetically mo- 

 saic, possessing one of the sex factors in 

 some of its nuclei and the other sex factor in 



