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of 'alue foi the classification of the Echini upon the whole, which 
are liable -to be preserved in the fossils — and Prof. Jackson is 
not free from vievving matters in this way either. Thus he does 
not ascnbe any classificatory valne to the minor structural details 
of pedicellariæ and spicules, which have proved to afford such a 
wonderful nchness of constant characters within several groups of 
Echinoids. If he had studied a fair number of recent forms also 
with regard to these structures, he would scarcely have failed to 
see that they do really afford characters of classificatory value 
wh.ch ought not to be neglected. He would then certainly not 
have confounded all the Diadema- species into one after the old 
fashiou, and neither would he then have maintained the genus 
Strongylocentrotus in the wide sense, in which Agassiz used it, 
but which scarcely any specialist on recent Echini of some con- 
sideration accepts any more. He would then e. g. have found, how 
the pedicellariæ and spicules are of a very characteristic structure 
m all those forms, where the gill-cuts are sharp and deep, which 
decidedly mdicates that these forms are really nearer related to 
each othei. I must emphasize again, as I have done before, 
that all characters must be taken into consideration, when the 
real interrelations of the Echini (- or any other kind of animals _) 
are sought for. Jackson certainly states that “every part of an 
organism is worthy of careful study“, but he adds immediately that 
“to base classification on such minutiae of no bnown evolutionary 
value is undesirable” (p. 199). I caunot but regard it as inad- 
missible to declare beforehand some structure or other as of no 
value for classification. If it is found that the microscopic structure 
of pedicellariæ and spicules are of classificatory value among the 
recent Echini, the necessary conclusion is that the fossil forms are 
in this respect incompletely preserved (— even though the pedi- 
cellariæ may sometimes be found preserved also in the fossil forms, 
as has now been found by Jackson even in a Palæozoic form’ 
Meekechinus elegant -). Neither is it admissible to claim the’ 
uselessness of such structures, because they offer perhaps some 
