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 the identification. 
It may not be superfluous, however, to state that I do not 
think the pedicellariæ had any essential bearing on the classification 
of the Palæozoic Echini. The structural features of the test are 
there so wonderfully diversified that we have therein the best 
possible guide to their affinities, and Jackson has made use of 
this 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 here the microscopical 
structures are neglected, the result becomes the association of a 
number of, in reality, widely different forms in a single genus, as 
« Echinus” and ""Strongylocentrotus”, or family, as the ””Strongylo- 
centrotidæ”. Here Jackson's classification in my opinion decidedly 
represents a step backwards. 
One of- the most important conclusions with regard to the 
morphology of the test of the Echini arrived at by Professor 
Jackson. is this, that the interambulacra have not the value of 
a separate morphological part of the test corresponding to the am- 
bulacra; the test (corona) is not, as generally supposed, divided 
into 10 areas, 5 ambulacra and 5 interambulacra, but only into 5 
areas, each consisting of an ambulacrum joined along each side by 
a half-interambulacrum. The interambulacral plates do not develop 
at the sides of the genital plates, but at the sides of the ocular 
plates. Accordingly the genital plates are regarded as being only 
of secondary importance in Echinoid morphology. The arguments 
produced for this quite new and rather startling conclusion are 
especially some remarkable cases of abnormal variations in the 
regular Echini; also the absence of genital 5 in Spatangoids is 
regarded as leading towards this conclusion. 
There may, however, be raised some objections to this. I 
would first say that it seems to me rather unsafe to base so im- 
