96 The Unity of the Organism 



mon in the animal kingdom. Figure 56, a photograph of 

 the skeleton of a python (see frontispiece), shows in a gen- 

 eral way the size-relations of metameric skeletal parts in a 

 higher vertebrate. Something of the extent to which the 

 proportionality of parts of the individual metameres is car- 

 ried out in this skeleton is shown by tabulating a series of 

 measurements of the parts : 



"Position of vertebra" refers to the serial number, beginning 

 with the head-end, of the vertebra measured. Legend: L.V., 

 Length of vertebra, measured from the posterior edge of one 

 dorsal spine to the anterior edge of the one next behind it. T.V., 

 thickness of vertebral centrum in its thinnest part, i.e., near the 

 middle. T. ex. zyg., thickness of vertebra at extreme of posterior 

 zygopophyses (articulating processes). H.D.S., height of dorsal 

 spine. W.D.S., width of dorsal spine. L.R., length of rib. 



The starfishes are another class of animals which exhibit 

 beautifully this size gradation of repeated parts, both their 

 "tube-feet" and the calcareous skeletal supports being 

 graded proportionately to the tapering arms of the animal. 

 The following table presents a series of measurements of the 

 two organ systems just mentioned, from a single arm of 

 Astrospecten calif ornicus. The dimensions are in millimet- 

 ers, and the series proceed from the proximal to the distal 

 end of the arm. 



