174 THE CHROMOSOMES 



in other nematodes, where many small chromosomes 

 are present, such a loss has been observed from all 

 of the chromosomes, which nevertheless retain their 

 constancy of number in the germ cells. 



It is not without interest to find in these 

 Nematodes with many small chromosomes that the 

 female and the male have constantly different 

 numbers of chromosomes (Edwards, Gulick, Schleip) 

 — the additional ones corresponding to the extra 

 chromosomes of Ascaris. Thus Edwards finds in 

 Ascaris lumbricoides : 



43 chromosomes in the male =19 + 5 (egg) + 19 

 (male producing-sperm) 



48 chromosomes in the female =19 + 5 (egg) 

 19 + 5 (female producing-sperm) 



In Ascaris incurva, Goodrich has shown (Fig. 36 

 M) that a sex chromosome complex consisting of 7 

 X-chromosomes goes to one pole of the spindle, so 

 that the female-producing sperm has 21 chromo- 

 somes; and the male-producing only 14. At the 

 time of reduction the X-chromosome complex of 

 7 elements shows a tendency to unite more or less 

 into a compound element (Fig. 36 M). 



Tetraploidy 



The fact that ''pairs of species" are known, one 

 characterized by having twice the number of chro- 

 mosomes of the other, has suggested that new types 

 may arise through doubling of the chromosome 

 number. The double chromosome types are larger 



