PRELIMINARY NOTE ON GAMETOGENESIS IN 

 PHILOSAMIA CYNTHIA. 



PAULINE H. DEDERER. 



Since the history of the chromosome groups has been so com- 

 pletely worked out in the spermatogenesis of insects, and the fact 

 well established of an almost universal dimorphism in the'sperma- 

 tozoa, it has become increasingly important to study the condi- 

 tions of maturation in the eggs of insects. It has been assumed 

 that in insecta the eggs are all alike in the number and behavior of 

 the chromosomes, and the recent observations of Morrill ('10) 

 and others have shown this to be the case. 



In studying the history of the male germ cells in the moth 

 Philosamia cynthia, the writer found ('07) that the diploid chro- 

 mosome groups are reduced to exactly similar haploid groups in 

 the spermatocyte divisions. The same facts were determined 

 by Stevens ('05) and Cook ('10) for various other Saturnidae. 



Since no dimorphism was observed in the chromosome groups 

 of the male, the possibility suggested itself that dimorphism 

 might be found in the eggs. Large numbers of cynthia eggs 

 were examined to determine the behavior of the chromosomes 

 in maturation, with especial reference to the question of di- 

 morphism. The results may be briefly stated as follows: 



The number of chromosomes in the somatic cells is 26, which 

 is also the spermatogonial number. The reduced number of 

 chromosomes is found in the eggs just before they are laid. At 

 this stage of late prophase, 13 chromosomes lie enclosed within 

 the nuclear membrane, near the surface of the egg. The chromo- 

 somes are smooth, elliptical or dumb-bell-shaped bodies, well 

 separated from one another. They show only slight differences 

 in size and form. When arranged on the first polar spindle in 

 anaphase, each of the dyad chromosomes separates into equal 

 parts, which move to opposite poles of the spindle. In several 

 hundreds of eggs examined, all the chromosome groups appeared 

 similar. The chromosomes remaining in the egg are again halved 



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