302 FERNANDUS PAYNE. 



structure in Galgulus and hence cannot definitely say what it is. 

 It is possible that it is formed by the fusion of the five chromo- 

 somes which later appear in the pentad group of the second 

 division. 



At present there are not sufficient data to show the exact rela- 

 tion between this type of chromosome distribution and those 

 already described. For this reason, I shall not attempt to 

 homologize them in detail. Nevertheless, there is an evident 

 similarity between the behavior of the pentad group as a whole 

 and that of a single pair of idiochromosomes. In a general way, 

 the four chromosomes of this group which go to one pole have 

 the same relation to sex -production as a single large idiochromo- 

 some, while the one chromosome which goes to the other pole 

 may be compared to a small idiochromosome. 



With the discovery of this new type of differential chromo- 

 somes, it becomes more evident that the sexual differences of the 

 chromosomes, even in the same order of animals, by no means 

 conforms to a single numerical rule. In forms with one pair of 

 idiochromosomes, the two sexes have the same number of chro- 

 mosomes ; in those with the odd chromosome, the female has 

 one more than the male ; and in Galgulus, the female has three 

 more chromosomes than the male. 



In many forms, as has been shown by Montgomery, Sutton 

 and others, the spermatogonial and oogonial chromosomes may 

 be paired two by two in respect to their size relations. In Galgu- 

 lus, the chromosomes are too nearly equal in size to be readily 

 paired, and the differential chromosomes are indistinguishable 

 from the others. 



Since in Galgulus there are two classes of spermatozoa ; since 

 the spermatogonial number is thirty-five and the oogonial thirty- 

 eight, we have another support to add to the view that the two 

 classes of spermatozoa are respectively male and female pro- 

 ducing. In a recent paper, Correns has demonstrated by experi- 

 ment, that in some plants there are two kinds of male germ cells 

 produced in equal numbers, and that these two kinds are male 

 and female determinants. 



Zoological Laboratory, 

 Columbia University, 

 February 21, 1908. 



