Growth Integration 95 



Graded Repetitive Series as Integrative Phenomena 



This, perhaps the simplest form of integrational phenom- 

 ena known to biology, is seen almost everywhere, but shows 

 itself most typically and strikingly in plants and in many 

 lower animals. Reference is made to the gradation in the 

 repetitive or meristic parts appearing in so many organisms. 

 The most obvious criterion of such gradation is the rela- 

 tive size of the parts, but, as we shall see later, there is con- 

 siderable reason for supposing the gradation is not re- 

 stricted to size. The few examples to which space can be 

 given are selected to represent as wide a range as possible 

 of the phenomena under consideration. 



Illustrations from Anvmals 



The lancelets, fish-like animals of the genus Amptiioxus, 

 may be noticed first (Figure 55). It will be observed that 



FIGURE 55 SIDE VIEW OF AMPHIOXUS (AFTER PARKER & HASWELL). nch., 

 notochord. cir., cirri, or.hd., oral hood, myom., myomeres. dors.fr., 

 dorsal fin rays, cd.f., caudal fin. gon., gonads 



the creature tapers off toward both ends and that the series 

 of metameres, myom, usually called myomeres because they 

 compose the main body-musculature, diminish not only in 

 dorso-ventral measurement from near the middle each way, 

 but are also thickest in the mid-region and become thinner 

 as they progress toward each end. 



Something of this size scheme of body-parts is very com- 



