470 GEORGE H. CARPENTER. 
While he advocates the dismemberment of the Arthropoda 
into five separate phyla, I support strongly the older view 
that they must be regarded as a “natural”? monophyletic 
group. It must be admitted that most modern zoologists 
who have written on the subject incline towards the poly- 
phyletic origin of the Arthropoda, though they may not go 
so far as Packard in separating from each other the various 
classes [ Hutton, etc. (14)]. All the more cheering, therefore, 
has been Lankester’s vindication of the essential unity of the 
Arthropodan type, and in the ‘ Encyclopedia’ articles his 
position is even stronger than in the earlier paper (18) quoted 
in my recent essay. 
It may be objected that, with such differences of opinion 
as to the theoretical interpretation of well-known facts, 
further discussion must prove useless, and that fresh facts 
are needed before any secure conclusions can be reached. 
But, if the fundamental assumptions underlying all 
modern phylogenetic speculation be accepted, it 
seems to me that we have plenty of facts from which to arrive 
at a conclusion, and that our conclusion can only be 
Lankester’s. Unless zoologists as a whole have “ followed 
wandering fires,” in believing that ‘community of descent is 
the bond which is partially revealed to us by our classifica- 
tions,” they must surely admit that the “remarkable and 
distinctive features of structure which hold the Arthropoda 
together render it impossible to conceive of them as having a 
polyphyletic origin.” 
Those zoologists who wish to divide the Arthropoda into 
several distinct phyla constantly refer to the most obvious 
external features of the group—the hard, segmented exo- 
skeleton and jointed limbs—as conceivably due to “ converg- 
ence” or “homoplasy.” But such a superficial view over- 
looks the profoundly important internal characters which 
distinguish the Arthropoda: the reduced ccelom ; the heart 
with paired openings, leading from a “ pericardium” made up 
of greatly enlarged blood-spaces ; the mesodermal excretory 
tubes; the apparent absence of true nephridia; the absence 
