136 THE BIOLOGY OF tWl'NS 



place. But before entering upon a discussion of somati- 

 segregation, we must needs study some of the data upon 

 which the theory is based. Only a few selected cases may 

 be presented within the scope of the present volume; the 

 reader is referred for complete data to two recent papers.^ 



For convenience of presentation it is necessary to 

 conventionalize the figures of band and scute doubling. 

 The methods of representing band doubhngs together- 

 with the detail of actual cases are shown in Fig. 42. 

 At the top of the page is shown a single band with an 

 extensive doubhng involving all but a few marginal 

 units at the right and the left. Directly underneath 

 is a conventional representation with numbers indicating 

 the numbers of scutes involved. Below this is another 

 type of doubhng in detail, with the conventional repre- 

 sentation just beneath. Various types of scute doubling 

 are shown also, and the method of indicating the location 

 and distribution of them is by placing a small diagram 

 of a double scute in a band and locating its position 

 with reference to margin or middle by a number. In 

 doubtful cases an arrow points to the spot from which 

 the count proceeds. 



The character and distribution of inherited band 

 and scute doubling may be illustrated by a complete 

 detail drawing of the affected bands in one set of fetuses 

 (set K 87) and their mother (Fig. 42). The affected 

 band of the mother is marked M and those of the four 

 fetuses I, II, III, and IV. Fetuses I and II (a pair) 

 have each two affected bands. It will be seen that the 

 mother has a unilateral doubling involving 13-14 

 scutes six places from the left-hand margin of band i. 



' H. H. Newman, he. cit. 



