130 



The Nucleus and Cytoplasm in Development 



lEaploidy. The effects on development of 

 the presence of a single set of chromosomes, 

 either the maternal or the paternal, have 

 been investigated extensively. Haploid em- 

 bryos may be obtained in various types of 

 experiments which are all designed to cir- 

 cumvent the reconstitution of the normal 



axolotls, haploid white embryos have ap- 

 peared spontaneously among offspring from 

 reciprocal combinations, white 9 X black 

 fe , and black 9 X white S. This demon- 

 strates that either the egg nucleus or the 

 sperm nucleus may be functioning and con- 

 tribute the haploid set of chromosomes, al' 



Table 5. Development of non-nucleated eggs or egg fragments* 



CLEAVAGE AND FINAL 

 METHOD 



STAGE REACHED 



Aste rias Jorbesii 



Arbacia punctulata 



Arbacia pustulosa 



Parechinus micro- 



tuberculatus 



Paracentrolus lividus 

 Sphaerechinus 



granulans 

 Chaetopterus 



pergamentaceus 

 Amblystoma mexi- 



canum (axolotl) 



Rana pipiens 



Triturus palmatus, 

 T. viridescens 



Removal of maturation spindle from 

 unfertilized egg, treatment with COo 

 to induce parthenogenesis (formation 

 of cytasters) 



Fragmentation of unfertilized egg by 

 centrifuging, hypertonic treatment of 

 non-nucleated halves or quarters to 

 induce parthenogenesis (formation of 

 cytasters) 



Same 

 Same 



Same 

 Same 



Same 



Removal of maturation spindle by 

 puncture of egg, spontaneous degen- 

 eration of single sperm nucleus; 

 sperm aster probably functioned in 

 cleavage 



Eggs inseminated with heavily x-rayed 

 sperm of R. catesbiana, maturation 

 spindle removed by puncture; sperm 

 nucleus damaged, did not take part 

 in development, sperm aster probably 

 functioned 



Polyspermy and removal of maturation 

 spindle by division or puncture of egg, 

 abnormal mitotic figures and cytas- 

 ters appear frequently, both sperm 

 asters and cytasters may function in 

 cleavage 



Irregular cleavage to McClendon, 

 "morula" 



More or less regular Harvey, '36, '40 



cleavage to blastula 



without blastocoele 



(up to 500 cells), 



Fig. 27a 

 16 cells Harvey, '38 



Irregular cleavage or 



fragmentation to 



blastula-like structure 

 Same 



Eggs fragment irregu- 

 larly 

 2 cells Harvey, '39 



Advanced, normal Stauffer, '45 



blastula with blas- 

 tocoele (single case), 

 Fig. 276 



Partial blastulae, some Briggs, Green and 

 cells with degener- King, '51 

 ated remnants of pa- 

 ternal chromatin, 

 Fig. 21c 



Advanced blastulae Fankhauser, '29, '34; 



with large areas of Fankhauser and 

 non-nucleated cells Moore, '41 



* See Figure 27. 



diploid chromosome complement during fer- 

 tilization (Fig. 28, Table 6). Whether the 

 unfertilized egg is stimulated to partheno- 

 genetic development by artificial activation, 

 or the fusion of the egg and sperm nuclei is 

 prevented in the fertilized egg (gynogenesis, 

 androgenesis) seems to have little influence 

 on the results. Recently it has been shown 

 that haploid embryos may develop spon- 

 taneously from untreated eggs of various 

 species of salamanders, with a frequency of 

 between one or two in a thousand. In crosses 

 between recessive white and dominant black 



though the egg nucleus seems to be involved 

 in the majority of cases (Humphrey and 

 Fankhauser, unpublished). 



While haploid embryos have often been 

 obtained from eggs of echinoderms, annelids, 

 mollusks, and ascidians, their development 

 has not been followed beyond early larval 

 stages. The analysis of the later manifesta- 

 tions of haploidy has been largely confined 

 to various species of amphibians. Regardless 

 of the method used to induce haploidy, the 

 development of the haploid embryos is usu- 

 ally retarded and abnormal from an early 



