A NEW AND ANNEOTANT TYPI^ 01-' CfllLOPOD. 431 



evident that the similarity, exact though it be, between the 

 fifteen leg-bearing somites of Lithobius and the anterior 

 fifteen leg-bearing somites of Scolopendra, with respect to 

 the alternation in size of tergal plates and the number and 

 disposition of stigmata, is the outcome of homoplasy and not 

 of homology. 



Startling as this proposition may at first seem, the difficulties 

 in the way of its comprehension are not insuperable. 



Accepting the comparison between the somites of the two, 

 as tabulated above, and assuming, as is justifiable, that the 

 stigmata occurring upon the first, third, and tenth somites of 

 the Lithobioid type and unrepresented on the corresponding 

 somites of the Scolopendroid type have not been independently 

 acquired in the former case, we are forced to conclude that 

 the Scolopendroid type itself has been derived from a form 

 possessing stigmata at least upon the first, third, fourth, fifth, 

 seventh, eighth, tenth, twelfth, fourteenth, fifteenth, six- 

 teenth, eighteenth, and twentieth somites, since stigmata are 

 found upon these somites either in the Scolopendroid type 

 or upon their hypothetical equivalents in the Lithobioid. 



It is possible, however, to go a step further. Since all the 

 Geophilomorpha, without exception, and one, in this respect, 

 aberrant genus of Scolopendromorpha, namely Plutonium, 

 possess stigmata upon all the leg-bearing metameres except 

 the first and last, it is no strain upon probability to assume that 

 the primitive Scolopendromorph was furnished with stigmata 

 upon all the leg- bearing somites except the last. Further- 

 more, since stigmata are found only upon major somites, it 

 follows that all the somites were originally of that kind. 

 This contention is fortified by the consideration that simi- 

 larity in size and structure of the individual segments of a 

 series is one of the first laws of metamerism. 



Hence, although it may be impossible to give a physio- 



ogical explanation of the fact, no difliculty on morphological 



grounds obstructs the acceptance of the opinion that a typical 



Scolopendroid, like Rhysida, with stigmata only upon the 



third, fifth, seventh, eighth, tenth, twelfth, fourteenth, six- 



