PARTHENOGENETIC DEVELOPMENT OF STARFISH EGG. 3 I 5 



As I have already stated, owing to my inability to make an 

 accurate count, I have not been able to show this to be true in 

 the case of the egg whose reduced number of chromosomes is 18. 

 That the behavior of both eggs is probably similar will be granted 

 by most readers. 



General Considerations. 



These observations show conclusively that in the fertilized egg 

 there is no conjugation of maternal and paternal chromosomes as 

 individuals, at the time when I thought that such a union might 

 take place. 



The facts that I have given, namely, that the reduced number 

 of chromosomes in the male germ cell of one form is 9, that the 

 reduced number of chromosomes in one egg is 18, and that the 

 number in fertilized eggs is 18 and 36 is sufficient proof. 



After the examination of many lots of fertilized eggs I became 

 convinced that 18 and 36 were not constant as somatic numbers. 

 Small variations, such as differences of one or two, might be laid 

 to error in counting. A constant greater variation that I have 

 found hardly seems due to the same cause. 



A possible interpretation of such a greater variation is of 

 interest. 



In one lot of eggs the number 27 seems constant. In this 

 lot I have never been able to count as many as 36 chromosomes. 



Such a number, (27), is readily explained on the supposition 

 that an egg containing 18 chromosomes has been fertilized by a 

 spermatozoan containing 9, or that an egg with 9 has been fer- 

 tilized by a spermatozoan containing 18. The result in either 

 case would be a somatic number of 27. 



Now, accepting the interpretation of synapsis as the conjuga- 

 tion of homologous maternal and paternal chromosomes, we 

 shall have at the conclusion of synapsis a reduced number of 18. 

 That is, nine pairs or nine bivalant chromosomes and nine univa- 

 lents which had been unable to find mates. 



Such eggs, if they were fertilized by a spermatozoan containing 

 18 chromosomes should give rise to individuals with a somatic 

 number of 36, or, uniting with a spermatozoan with 9 chromo- 

 somes should retain a somatic number of 27. 



