734 INHERITANCE 



two species were employed, and of each species there were two varieties. 

 Polytoma uvella is eUipsoidal in form, with no papilla at the anterior end 

 (between the places of attachment of the two flagella). In one variety 

 there is a large eyespot, in the other there is no eyespot (see Fig. 169 A, 

 B ) . In P. pascheri the form is a long oval, there is a papilla between the 

 flagellar attachments, and there is no eyespot. One variety is large, the 

 other very small (Fig. 169 C, D). 



In the four varieties there are thus differences in four pairs of char- 

 acters. Moewus designates these characters as follows: 



Form of body: ellipsoidal, F (as in P. uvella) 



long oval, f (as in P. pascheri) 

 Papilla: present, P 



absent, p 

 Eyespot: present, S 



absent, s 

 Size: large, D 



small, d 



Using these designations, the four varieties may be represented by 

 formulae as follows: 



P. uvella, with eyespot, FpSD 



without eyespot, FpsD 

 P. pascheri, large, fPsD 

 small, fPsd 



Any of these four varieties may be crossed with any other, so that six 

 different crosses are possible. Each of the varieties has eight chromo- 

 somes, so that any cross forms a zygote with sixteen chromosomes. From 

 each zygote arise, by the two maturation divisions, four swarm cells. 

 These four, after becoming free, multiply vegetatively to form clones. 

 All the individuals of each clone show the same characteristics as does 

 the swarm cell from which the clone is derived, so that we may speak 

 indifferently of the characteristics of each of the four swarm cells, or of 

 each of the four clones derived from them. 



When two varieties that differ in a single pair of characters are crossed, 

 two of the four swarm cells produced show one of these characters, the 

 other two the other character. Thus P. uvella with eyespot, S, is crossed 

 with P. uvella without eyespot, s. Of the four swarmers arising from the 



