214 
difficulty for study. If such a principle had to prevail in classi¬ 
fication, I wonder what e. g. the students of Nemerteans would say, 
who must cut their objects into sections, before they can reach 
certainty in tbe identification. 
It may not be superfiuous, however, to State tbat I do not 
think tbe pedicellariæ bad any essential bearing on tbe classification 
of tbe Palæozoic Echini. The structural features of the test are 
there so wonderfully diversified that we have therein tbe best 
possible guide to their affinities, and Jack son bas made use of 
tbis guide in the best possible way. A quite different thing is it 
in such highly specialized groups as the Camarodonta, where the 
test structure is of great uniformity. If bere tbe micioscopical 
structures are neglected, the result becomes the association of a 
nuinber of, in reality, widely different forms in a single genus, as 
“Echinus ’’ and “ Strongylocentrotus ’, or family, as the ‘‘Strongylo- 
centrotidæ”. Here Jack son’s classification in my opinion decidedly 
represents a step backwards. 
One of tbe most important conclusions witb regard to the 
morphology of the test of the Echini arrived at b} Piofessoi 
Jackson is tbis, tbat tbe interambulacra have not tbe value of 
a separate morphological part of tbe test corresponding to the ani- 
bulacra; the test (corona) is not, as generally supposed, divided 
into 10 areas, 5 ambulacra and 5 interambulacra, but only into 5 
areas, eacb consisting of an ambulacrum joined along eacb side by 
a half-interambulaerum. The interambulacral plates do not develop 
at the sides of tbe genital plates, but at tbe sides of the oculai 
plates. Accordingly tbe genital plates are regarded as being onl) 
of secondary importance in Echinoid morphology. The arguments 
produced for this quite new and rather startling conclusion aie 
especially some remarkable cases of abnormal variations in tbe 
regular Echini; also tbe absence of genital 5 in Spatangoids is 
regarded as leading towards tbis conclusion. 
There may, however, be raised some objections to tbis. I 
would first say that it seems to me rather unsafe to base so im- 
