82 MITOSIS : THE VARIATION OF THE CHROMOSOMES 



Animals 



Aggregata eberthi (Sporozoa) 

 Drosophila melanogaster (Diptera) 



Dobell, 1925 ; Belar, 1926. 

 Bridges, 1927 ; Morgan et 

 al., 1925. (See Fig. 121.) 

 de Winiwarter, 1931. 

 Beliajeff, 1930. 



Saez, 1930 ; cf. White, 1933. 

 Matthey, 1929, 1931, 1933. 

 Nakamura, 1931. 

 Cf. Werner, 1931 ; White, 

 1932 ; Roller, unpub. 



Tettigonia alhifrons (Locustidae) 

 Dasychira pudihunda (Lepidoptera) 

 Schistocerca paranensis (and other 



South American Acrididae) 

 Vipera aspis (Reptilia) 

 Eumeces latiscutatus (Reptilia) . 

 Meleagris gallopavo (and other 



Galliformes and Anseriformes). 



In some of these species the small chromosomes in the comple- 

 ments are variable in number. They are perhaps unessential to 

 the species, like the results of recent fragmentation already described. 



To turn to the comparison of different species, the lowest 

 chromosome numbers are found in the nematode Ascaris 

 megalocephala, which has two races, one with one haploid 

 chromosome, the other with two ; and in the Agaricaceae 

 (Wakayama, 1930), where species with two as their haploid number 

 occur. In the flowering plants, nine species are known which have 

 three as their haploid number, viz., Crepis capillaris (cf. Babcock 

 and Navashin, 1930), Callitriche autumnalis (j0rgensen, 1923), 

 Zacintha verrucosa (Navashin, 1930), and six Crocus species (Mather, 

 1932, and Fig. 16). The Table (10) shows the range in size and 

 numbers found in living organisms. It will be seen that the 

 approximate ranges found in the various constants, represented as 

 proportions, are as follows : — 



Breadth, i : 10 ^"^ 



Length, i : 10^'' 



Bulk: 



Chromosome, i 

 Complement, i 



Number, i : lo^ 



10-= 



10 



4 1 



(SphcBromyxa : Camhanis) 

 (Saprolegnia : Hyacinthus) 



(Drosera : Drosophyllum) 

 (Saprolegnia : Aulacantha) 

 (Ascaris : Aulacantha) 



It is clear that such great differences in structure and number 

 demand the assumption of both structural and genotypic change. 



