The Role of Nucleus and Cytoplasm 



131 



Fig. 28. Diagrammatic representation of the four types of experiments producing haploid embryos (see 

 Table 6). 



a. Parthenogenesis. Unfertilized egg is activated by artificial means and develops with haploid chromo- 

 some set of egg nucleus. 



b. Gynogenesis. Fertilized egg develops with egg nucleus alone; sperm nucleus degenerates but sperm 

 aster usually functions as division center. 



c, Androgenesis. Egg nucleus is removed from fertilized egg; haploid sperm nucleus alone takes part in 

 development. 



d, Andro-merogony. Fertilized egg is divided into two parts; right-hand half develops with sperm nucleus; 

 left-hand half with egg nucleus rarely cleaves normally because of lack of active division center {"gyno- 

 merogony"). 



stage on. In many cases the development of 

 the archenteron is subnormal, leading to 

 various degrees of microcephaly. The body 

 remains short and broad, blood circulation is 

 usually deficient, edema and ascites are com- 

 mon, and motility and general reactivity are 

 reduced. The great majority of embryos die 

 before they reach the feecling stage. How- 

 ever, there is evidence of specific differences 

 in the tolerance of haploidy (Fig. 29). On 

 the whole, embryos of various species of 

 newts are less affected than those of the 

 axolotl and of frogs and toads. 



Occasionally, haploid larvae appear that 

 are almost free from the usual symptoms 

 and begin to feed. The most advanced hap- 

 loid animals obtained so far were a Triturus 

 taeniatus developed from an egg fragment 

 (Baltzer, '22; Fankhauser, '37, '38a) which 



died at the end of metamorphosis at the age 

 of 100 days; a Triturus alpestris developed 

 from a refrigerated whole egg (Fischberg, 

 '44, '47a) which lived longer (290 days) but 

 was more retarded and died at the beginning 

 of metamorphosis; and, from refrigerated 

 eggs of Triturus granulosus, two larvae which 

 never metamorphosed and were fixed in 

 vigorous condition at 139 and 146 days of 

 age, respectively (Costello and Holmquist, 

 unpub.). A detailed study of the microscopi- 

 cal anatomy of the first-mentioned haploid 

 showed that the complex transformation 

 from the larva to the terrestrial salamander 

 with most of the characteristics of the adult 

 had taken place normally. In most organs, 

 the reduction of the size of the individual 

 cells to about one-half of the normal diploid 

 size was only in part compensated by an 



