SEGMENTATION AND PHYLOGENY OF ARTHROPODA. 471 
of ciliated epithelium; the possession of striated muscular 
tissue. And if it be objected that any of these are the neces- 
sary accompaniments of a hard exoskeleton and jointed 
limbs, let it be remembered that all of them (except the two 
last-mentioned)' are displayed by that class of Arthropoda 
(the Malacopoda) whose members are not arthropodous. I 
must confess that to me belief in the polyphyletic origin of 
the Vertebrata, the Echinoderma, or the Mollusca might be 
maintained with as great—or as little—reason as belief in 
the multiple descent of the Arthropoda. 
Numerical Correspondence in Segmentation. 
In my own recent essay the endeavour was made to prove 
an exact numerical correspondence in segmentation between 
typical Crustacea, Insecta, and Arachnida. The establish- 
ment of such a fact would conclusively demonstrate that the 
Arthropoda are monophyletic, since the independent origin 
of three classes of similarly formed animals with exactly the 
same number of primitive segments is surely incredible. In 
trying some years ago to trace homologies between the 
appendages of the Crayfish, Cockroach and Scorpion, I was 
astonished at the apparent identity in the number of segments 
in those three animals, and it was with much gratification 
that I afterwards found the same correspondence to have 
been suggested by Huxley (15) nearly fifty years ago, when 
he wrote: “I venture to think it a matter of no small moment 
if it can be proved that a Lobster, a Cockroach and a Scorpion 
are composed of the same primitive number of somites.” 
The facts and arguments that can be brought forward in 
favour of this contention have been set forth in my recent 
paper with considerable detail. The appended table showing 
the correspondence in segmentation between members of the 
various arthropod classes will serve for the present occasion 
as a sufficient summary of the evidence, and the references 
will enable those interested to estimate the authority on 
1 Hewitt has, however, lately pointed out that the muscle-fibres which work 
the jaw-levers of Peripatus are striated (‘ Manchester Memoirs,’ vol. |, p. 4). 
